Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Sep. 30, 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	898
Percentage of Gross Unrealized Losses Depressed Less than Twenty Percent of Cost or Amortized Cost	96.00%
ABS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	$ 44	$ 398
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	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	44	407
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	3
CLOs
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	1,193	679
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10	2
12 Months or More FV	741	923
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10	6
Total FV	1,934	1,602
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	20	8
CMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	533	538
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	27	7
12 Months or More FV	16	20
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4	6
Total FV	549	558
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	31	13
Corporate
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	1,609	789
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	56	9
12 Months or More FV	202	328
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26	16
Total FV	1,811	1,117
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	82	25
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	79	101
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	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	79	130
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	0
Municipal
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	478	222
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	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	478	222
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	7	2
RMBS
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	514	614
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	3
12 Months or More FV	29	68
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total FV	543	682
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	3
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Less Than 12 Months FV	28	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	28	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	4,478	3,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	102	26
12 Months or More FV	988	1,411
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	40	29
Total FV	5,466	4,840
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 142	$ 55