Accumulated Other Comprehensive Income Loss - AOCI Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 18,556
Other comprehensive income (loss), net of tax	$ (263)	$ 377	(863)	$ 804
Ending balance	17,862	17,802	17,862	17,802
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	2,204	2,055	2,834	1,684
OCI before reclassifications	(231)	388	(816)	842
Amounts reclassified from AOCI	(43)	(12)	(88)	(95)
Other comprehensive income (loss), net of tax	(274)	376	(904)	747
Ending balance	1,930	2,431	1,930	2,431
AOCI, Gain (Loss), Debt Securities, Available-for-sale, with Allowance for Credit Loss, Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2)	(2)	(2)	(3)
OCI before reclassifications	0	0	0	1
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss), net of tax	0	0	0	1
Ending balance	(2)	(2)	(2)	(2)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	12	48	12	9
OCI before reclassifications	8	(10)	22	37
Amounts reclassified from AOCI	(7)	(7)	(21)	(15)
Other comprehensive income (loss), net of tax	1	(17)	1	22
Ending balance	13	31	13	31
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	46	27	43	34
OCI before reclassifications	(4)	6	(1)	(1)
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss), net of tax	(4)	6	(1)	(1)
Ending balance	42	33	42	33
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,690)	(1,649)	(1,717)	(1,672)
OCI before reclassifications	1	0	(1)	(1)
Amounts reclassified from AOCI	13	12	42	36
Other comprehensive income (loss), net of tax	14	12	41	35
Ending balance	(1,676)	(1,637)	(1,676)	(1,637)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	570	479	1,170	52
OCI before reclassifications	(226)	384	(796)	878
Amounts reclassified from AOCI	(37)	(7)	(67)	(74)
Other comprehensive income (loss), net of tax	(263)	377	(863)	804
Ending balance	$ 307	$ 856	$ 307	$ 856

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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