Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	1,057
Percentage of Gross Unrealized Losses Depressed Less than Twenty Percent of Cost or Amortized Cost	98.00%
ABS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	204	44
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	204	44
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	0	0
Collateralized Loan Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	842	758
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	159	715
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	1,001	1,473
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	1	7
CMBS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	17
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	298	410
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	6	4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	87	19
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	385	429
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	9	21
Corporate
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	34	13
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,229	466
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	18
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	208	212
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,437	678
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	42	31
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	265	24
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	265	24
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	3	0
Municipal
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11	1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	695	34
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	12	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	707	34
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	11	1
RMBS
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	880	461
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	100	21
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	980	482
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	11	3
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	17	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,707	39
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	2,710	39
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	17	0
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	77	36
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	8,120	2,236
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	17	27
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	569	967
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	8,689	3,203
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	$ 94	$ 63

Percentage of gross unrealized losses depressed less than twenty percent of cost or amortized cost.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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