Level 4~Investments - Unrealized Losses on AFS Securities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	$ 13,984	$ 6,798
Amortized Cost
12 Months or More	2,026	2,040
Total	16,010	8,838
Fair Value
Less Than 12 Months	13,707	6,739
12 Months or More	1,910	1,969
Total	15,617	8,708
Unrealized Losses
Less Than 12 Months	(277)	(59)
12 Months or More	(116)	(71)
Total	(393)	(130)
ABS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	520	461
Amortized Cost
12 Months or More	33	30
Total	553	491
Fair Value
Less Than 12 Months	515	460
12 Months or More	32	29
Total	547	489
Unrealized Losses
Less Than 12 Months	(5)	(1)
12 Months or More	(1)	(1)
Total	(6)	(2)
CDOs
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	905	359
Amortized Cost
12 Months or More	0	1
Total	905	360
Fair Value
Less Than 12 Months	903	359
12 Months or More	0	1
Total	903	360
Unrealized Losses
Less Than 12 Months	(2)	0
12 Months or More	0	0
Total	(2)	0
CMBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	1,701	1,178
Amortized Cost
12 Months or More	242	243
Total	1,943	1,421
Fair Value
Less Than 12 Months	1,662	1,167
12 Months or More	224	228
Total	1,886	1,395
Unrealized Losses
Less Than 12 Months	(39)	(11)
12 Months or More	(18)	(15)
Total	(57)	(26)
Corporate
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	5,931	2,322
Amortized Cost
12 Months or More	1,066	1,064
Total	6,997	3,386
Fair Value
Less Than 12 Months	5,785	2,302
12 Months or More	1,002	1,028
Total	6,787	3,330
Unrealized Losses
Less Than 12 Months	(146)	(20)
12 Months or More	(64)	(36)
Total	(210)	(56)
Foreign government/government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	552	244
Amortized Cost
12 Months or More	51	51
Total	603	295
Fair Value
Less Than 12 Months	539	242
12 Months or More	48	49
Total	587	291
Unrealized Losses
Less Than 12 Months	(13)	(2)
12 Months or More	(3)	(2)
Total	(16)	(4)
Municipal
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	2,077	511
Amortized Cost
12 Months or More	230	236
Total	2,307	747
Fair Value
Less Than 12 Months	2,044	507
12 Months or More	214	228
Total	2,258	735
Unrealized Losses
Less Than 12 Months	(33)	(4)
12 Months or More	(16)	(8)
Total	(49)	(12)
RMBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	1,448	889
Amortized Cost
12 Months or More	132	137
Total	1,580	1,026
Fair Value
Less Than 12 Months	1,421	887
12 Months or More	127	135
Total	1,548	1,022
Unrealized Losses
Less Than 12 Months	(27)	(2)
12 Months or More	(5)	(2)
Total	(32)	(4)
US Treasury Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost	850	658
Amortized Cost
12 Months or More	272	254
Total	1,122	912
Fair Value
Less Than 12 Months	838	652
12 Months or More	263	250
Total	1,101	902
Unrealized Losses
Less Than 12 Months	(12)	(6)
12 Months or More	(9)	(4)
Total	$ (21)	(10)
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost		6,622
Amortized Cost
12 Months or More		2,016
Total		8,638
Fair Value
Less Than 12 Months		6,576
12 Months or More		1,948
Total		8,524
Unrealized Losses
Less Than 12 Months		(46)
12 Months or More		(68)
Total		(114)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Amortized Cost		176
Amortized Cost
12 Months or More		24
Total		200
Fair Value
Less Than 12 Months		163
12 Months or More		21
Total		184
Unrealized Losses
Less Than 12 Months		(13)
12 Months or More		(3)
Total		$ (16)