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Employee Benefit Plans - Defined Benefit Plan, Information about Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	$ 0	$ 0
Corporate | Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	0	0
Residential mortgage-backed securities ("RMBS") | Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	0	0
Foreign government/government agencies | Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	0	0
Mortgage loans | Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	0	0
Other investments | Significant Unobservable Inputs (Level 3)
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Settlements	0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	3,914	3,344
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	3,914	3,344
Fair value of plan assets — end of year	4,363	3,914
Defined Benefit Plan, Fair Value of Plan Assets, Excluded Investment Payables	20	40
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	724
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	724
Fair value of plan assets — end of year	859	724
Pension Benefits | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	2,420
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	2,420
Fair value of plan assets — end of year	2,599	2,420
Pension Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	160	151
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	160	151
Realized gains (losses), net	(1)	3
Changes in unrealized gains, net	6	6
Purchases	56	7
Sales	(9)	(11)
Transfers into Level 3	0	4
Transfers out of Level 3	2	0
Fair value of plan assets — end of year	210	160
Pension Benefits | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	3,874
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	3,874
Fair value of plan assets — end of year	$ 4,343	3,874
Pension Benefits | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	40.00%
Pension Benefits | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	60.00%
Pension Benefits | Short-term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	$ 88
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	88
Fair value of plan assets — end of year	100	88
Pension Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	34
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	34
Fair value of plan assets — end of year	75	34
Pension Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	54
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	54
Fair value of plan assets — end of year	25	54
Pension Benefits | Short-term Investments [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Corporate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	2,085
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	2,085
Fair value of plan assets — end of year	2,342	2,085
Pension Benefits | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Corporate | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	2,058
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	2,058
Fair value of plan assets — end of year	2,303	2,058
Pension Benefits | Corporate | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	27	14
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	27	14
Realized gains (losses), net	0	3
Changes in unrealized gains, net	1	2
Purchases	14	7
Sales	(3)	(3)
Transfers into Level 3	0	4
Transfers out of Level 3		0
Fair value of plan assets — end of year	39	27
Pension Benefits | Residential mortgage-backed securities ("RMBS")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	61
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	61
Fair value of plan assets — end of year	42	61
Pension Benefits | Residential mortgage-backed securities ("RMBS") | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Residential mortgage-backed securities ("RMBS") | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	61
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	61
Fair value of plan assets — end of year	41	61
Pension Benefits | Residential mortgage-backed securities ("RMBS") | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0	1
Realized gains (losses), net	0	0
Changes in unrealized gains, net	0	0
Purchases	1	0
Sales	0	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value of plan assets — end of year	1	0
Pension Benefits | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	101
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	101
Fair value of plan assets — end of year	47	101
Pension Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	101
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	101
Fair value of plan assets — end of year	47	101
Pension Benefits | U.S. Treasuries | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Foreign government/government agencies
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	18
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	18
Fair value of plan assets — end of year	25	18
Pension Benefits | Foreign government/government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Foreign government/government agencies | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	17
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	17
Fair value of plan assets — end of year	16	17
Pension Benefits | Foreign government/government agencies | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1	2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1	2
Realized gains (losses), net	0	0
Changes in unrealized gains, net	0	0
Purchases	9	0
Sales	0	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	1	0
Fair value of plan assets — end of year	9	1
Pension Benefits | CMBS
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	32
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	32
Fair value of plan assets — end of year	30	32
Pension Benefits | CMBS | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | CMBS | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	32
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	32
Fair value of plan assets — end of year	30	32
Pension Benefits | CMBS | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Other Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	97
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	97
Fair value of plan assets — end of year	137	97
Pension Benefits | Other Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Other Fixed Income [Member] | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	96
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	96
Fair value of plan assets — end of year	137	96
Pension Benefits | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1
Fair value of plan assets — end of year	0	1
Pension Benefits | Mortgage loans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	131
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	131
Fair value of plan assets — end of year	161	131
Pension Benefits | Mortgage loans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Mortgage loans | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Mortgage loans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	131	133
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	131	133
Realized gains (losses), net	0	0
Changes in unrealized gains, net	4	4
Purchases	32	0
Sales	(6)	(6)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Fair value of plan assets — end of year	161	131
Pension Benefits | Domestic
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	430
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	430
Fair value of plan assets — end of year	513	430
Pension Benefits | Domestic | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	429
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	429
Fair value of plan assets — end of year	513	429
Pension Benefits | Domestic | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1
Fair value of plan assets — end of year	0	1
Pension Benefits | Domestic | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	261
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	261
Fair value of plan assets — end of year	271	261
Pension Benefits | International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	261
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	261
Fair value of plan assets — end of year	271	261
Pension Benefits | International | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	3,304
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	3,304
Fair value of plan assets — end of year	3,668	3,304
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	724
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	724
Fair value of plan assets — end of year	859	724
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	2,420
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	2,420
Fair value of plan assets — end of year	2,599	2,420
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	160
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	160
Fair value of plan assets — end of year	210	160
Pension Benefits | Private Market Alternatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	358
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	358
Fair value of plan assets — end of year	451	358
Pension Benefits | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	212
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	212
Fair value of plan assets — end of year	224	212
Pension Benefits | Other investments | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1	1
Realized gains (losses), net	(1)	0
Changes in unrealized gains, net	1	0
Purchases	0	0
Sales	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	1	0
Fair value of plan assets — end of year	0	1
Pension Benefits | Defined Benefit Plan, Equity Securities, Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1
Fair value of plan assets — end of year	1	1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	75	85
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	75	85
Fair value of plan assets — end of year	63	75
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	22
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	22
Fair value of plan assets — end of year	19	22
Other Postretirement Benefits | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	53
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	53
Fair value of plan assets — end of year	44	53
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	$ 0	0
Other Postretirement Benefits | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	30.00%
Other Postretirement Benefits | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation	70.00%
Other Postretirement Benefits | Short-term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	$ 3
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	3
Fair value of plan assets — end of year	2	3
Other Postretirement Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	3
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	3
Fair value of plan assets — end of year	2	3
Other Postretirement Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | Short-term Investments [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | Corporate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	18
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	18
Fair value of plan assets — end of year	16	18
Other Postretirement Benefits | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | Corporate | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	18
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	18
Fair value of plan assets — end of year	16	18
Other Postretirement Benefits | Corporate | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | Residential mortgage-backed securities ("RMBS")
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	12
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	12
Fair value of plan assets — end of year	9	12
Other Postretirement Benefits | Residential mortgage-backed securities ("RMBS") | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | Residential mortgage-backed securities ("RMBS") | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	12
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	12
Fair value of plan assets — end of year	9	12
Other Postretirement Benefits | Residential mortgage-backed securities ("RMBS") | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	20
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	20
Fair value of plan assets — end of year	16	20
Other Postretirement Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	20
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	20
Fair value of plan assets — end of year	16	20
Other Postretirement Benefits | U.S. Treasuries | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | CMBS
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1
Fair value of plan assets — end of year	1	1
Other Postretirement Benefits | CMBS | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	0
Fair value of plan assets — end of year	0	0
Other Postretirement Benefits | CMBS | Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets — beginning of year	1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets — beginning of year	1
Fair value of plan assets — end of year	1	1
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Maximum | Other Postretirement Benefits | Alternative assets
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