Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	978
Percentage of Gross Unrealized Losses Depressed Less than Twenty Percent of Cost or Amortized Cost	97.00%
ABS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	$ 99	$ 44
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 Months or More FV	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	99	44
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	0
CLOs
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	278	758
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	2
12 Months or More FV	458	715
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	5
Total FV	736	1,473
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	7
CMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	360	410
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	17
12 Months or More FV	127	19
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10	4
Total FV	487	429
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	18	21
Corporate
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	2,451	466
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	72	13
12 Months or More FV	300	212
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15	18
Total FV	2,751	678
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	87	31
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	173	24
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	0
12 Months or More FV	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	173	24
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	4	0
Municipal
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	796	34
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	19	1
12 Months or More FV	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	796	34
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	19	1
RMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	953	461
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	3
12 Months or More FV	13	21
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	966	482
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	9	3
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	560	39
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	0
12 Months or More FV	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	560	39
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3	0
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	5,670	2,236
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	115	36
12 Months or More FV	898	967
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26	27
Total FV	6,568	3,203
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 141	$ 63