Investments - Investments - Unrealized Losses on AFS Securities (Details) $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Unrealized Losses
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1,682
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]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	$ 143	$ 566
Amortized Cost
12 Months or More	108	113
Total	251	679
Fair Value
Less Than 12 Months	143	566
12 Months or More	107	112
Total	250	678
Unrealized Losses
Less Than 12 Months	0	0
12 Months or More	(1)	(1)
Total	(1)	(1)
CLOs
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	1,218	1,358
Amortized Cost
12 Months or More	82	7
Total	1,300	1,365
Fair Value
Less Than 12 Months	1,208	1,338
12 Months or More	81	7
Total	1,289	1,345
Unrealized Losses
Less Than 12 Months	(10)	(20)
12 Months or More	(1)	0
Total	(11)	(20)
CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	83	896
Amortized Cost
12 Months or More	1,391	1,129
Total	1,474	2,025
Fair Value
Less Than 12 Months	82	882
12 Months or More	1,359	1,079
Total	1,441	1,961
Unrealized Losses
Less Than 12 Months	(1)	(14)
12 Months or More	(32)	(50)
Total	(33)	(64)
Corporate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	737	7,174
Amortized Cost
12 Months or More	4,175	2,541
Total	4,912	9,715
Fair Value
Less Than 12 Months	722	6,903
12 Months or More	4,057	2,366
Total	4,779	9,269
Unrealized Losses
Less Than 12 Months	(15)	(271)
12 Months or More	(118)	(175)
Total	(133)	(446)
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	35	407
Amortized Cost
12 Months or More	292	203
Total	327	610
Fair Value
Less Than 12 Months	35	391
12 Months or More	285	193
Total	320	584
Unrealized Losses
Less Than 12 Months	0	(16)
12 Months or More	(7)	(10)
Total	(7)	(26)
Municipal
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	8	1,643
Amortized Cost
12 Months or More	285	292
Total	293	1,935
Fair Value
Less Than 12 Months	8	1,613
12 Months or More	278	275
Total	286	1,888
Unrealized Losses
Less Than 12 Months	0	(30)
12 Months or More	(7)	(17)
Total	(7)	(47)
RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	237	1,344
Amortized Cost
12 Months or More	985	648
Total	1,222	1,992
Fair Value
Less Than 12 Months	236	1,329
12 Months or More	973	628
Total	1,209	1,957
Unrealized Losses
Less Than 12 Months	(1)	(15)
12 Months or More	(12)	(20)
Total	(13)	(35)
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	153	497
Amortized Cost
12 Months or More	294	339
Total	447	836
Fair Value
Less Than 12 Months	153	492
12 Months or More	290	329
Total	443	821
Unrealized Losses
Less Than 12 Months	0	(5)
12 Months or More	(4)	(10)
Total	(4)	(15)
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	2,614	13,885
Amortized Cost
12 Months or More	7,612	5,272
Total	10,226	19,157
Fair Value
Less Than 12 Months	2,587	13,514
12 Months or More	7,430	4,989
Total	10,017	18,503
Unrealized Losses
Less Than 12 Months	(27)	(371)
12 Months or More	(182)	(283)
Total	$ (209)	$ (654)