Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2,204
Percentage of Gross Unrealized Losses Depressed Less than Twenty Percent of Cost or Amortized Cost	94.00%
ABS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	$ 1,045	$ 398
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	3
12 Months or More FV	0	9
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	1,045	407
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	26	3
CLOs
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	1,373	679
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	123	2
12 Months or More FV	616	923
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	56	6
Total FV	1,989	1,602
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	179	8
CMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	1,379	538
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	111	7
12 Months or More FV	18	20
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5	6
Total FV	1,397	558
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	116	13
Corporate
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	6,762	789
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	493	9
12 Months or More FV	183	328
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26	16
Total FV	6,945	1,117
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	519	25
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	439	101
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	23	0
12 Months or More FV	0	29
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	439	130
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	23	0
Municipal
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	719	222
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	30	2
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	719	222
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	30	2
RMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	1,604	614
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	60	3
12 Months or More FV	25	68
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	0
Total FV	1,629	682
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	62	3
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	45	88
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
12 Months or More FV	0	34
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	1
Total FV	45	122
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	1
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	13,366	3,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	866	26
12 Months or More FV	842	1,411
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	89	29
Total FV	14,208	4,840
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 955	$ 55