Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 0
Balance beginning of period	1,248	$ 1,594	$ 2,622
OCI before reclassifications	386	(498)	(1,693)
Deferred income tax benefit (expense)	(155)	160	619
AOCI before reclassifications, net of income tax	1,479	1,256	1,548
Amounts reclassified from AOCI	47	(13)	72
Deferred income tax benefit (expense) (2)	311	5	(26)
Amounts reclassified from AOCI, net of income tax	358	(8)	46
Balance end of period	1,837	1,248	1,594
Unrealized Investment Gains (Losses), Net of Related Offsets
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	330
Balance beginning of period	1,019	1,379	2,445
OCI before reclassifications	529	(565)	(1,759)
Deferred income tax benefit (expense)	(206)	185	643
AOCI before reclassifications, net of income tax	1,342	999	1,329
Amounts reclassified from AOCI	61	30	78
Deferred income tax benefit (expense) (2)	306	(10)	(28)
Amounts reclassified from AOCI, net of income tax	367	20	50
Balance end of period	1,709	1,019	1,379
Unrealized Gains (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning of period	258	241	183
OCI before reclassifications	(152)	70	95
Deferred income tax benefit (expense)	54	(25)	(33)
AOCI before reclassifications, net of income tax	160	286	245
Amounts reclassified from AOCI	(14)	(43)	(6)
Deferred income tax benefit (expense) (2)	5	15	2
Amounts reclassified from AOCI, net of income tax	(9)	(28)	(4)
Balance end of period	151	258	241
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance beginning of period	(29)	(26)	(6)
OCI before reclassifications	9	(3)	(29)
Deferred income tax benefit (expense)	(3)	0	9
AOCI before reclassifications, net of income tax	(23)	(29)	(26)
Amounts reclassified from AOCI	0	0	0
Deferred income tax benefit (expense) (2)	0	0	0
Amounts reclassified from AOCI, net of income tax	0	0	0
Balance end of period	$ (23)	$ (29)	$ (26)