Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period	$ 1,861	$ 2,811	$ 1,248	$ 1,594
OCI before reclassifications	(893)	(422)	9	1,440
Deferred income tax benefit (expense)	318	152	(18)	(504)
AOCI before reclassifications, net of income tax	1,286	2,541	1,239	2,530
Amounts reclassified from AOCI	(24)	(64)	52	(47)
Deferred income tax benefit (expense)	3	22	(26)	16
Amounts reclassified from AOCI, net of income tax	(21)	(42)	26	(31)
Balance, end of period	1,265	2,499	1,265	2,499
Unrealized Investment Gains (Losses), Net of Related Offsets
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period	1,675	2,540	1,019	1,379
OCI before reclassifications	(852)	(394)	106	1,369
Deferred income tax benefit (expense)	305	145	(52)	(479)
AOCI before reclassifications, net of income tax	1,128	2,291	1,073	2,269
Amounts reclassified from AOCI	(23)	(60)	65	(26)
Deferred income tax benefit (expense)	2	21	(31)	9
Amounts reclassified from AOCI, net of income tax	(21)	(39)	34	(17)
Balance, end of period	1,107	2,252	1,107	2,252
Unrealized Gains (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period	217	288	258	241
OCI before reclassifications	(50)	(15)	(101)	74
Deferred income tax benefit (expense)	17	5	35	(26)
AOCI before reclassifications, net of income tax	184	278	192	289
Amounts reclassified from AOCI	(1)	(4)	(13)	(21)
Deferred income tax benefit (expense)	1	1	5	7
Amounts reclassified from AOCI, net of income tax	0	(3)	(8)	(14)
Balance, end of period	184	275	184	275
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance, beginning of period	(31)	(17)	(29)	(26)
OCI before reclassifications	9	(13)	4	(3)
Deferred income tax benefit (expense)	(4)	2	(1)	1
AOCI before reclassifications, net of income tax	(26)	(28)	(26)	(28)
Amounts reclassified from AOCI	0	0	0	0
Deferred income tax benefit (expense)	0	0	0	0
Amounts reclassified from AOCI, net of income tax	0	0	0	0
Balance, end of period	$ (26)	$ (28)	$ (26)	$ (28)