Other Comprehensive Income - Changes in AOCI by Component (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					$ 6,504				$ 6,063	$ 6,504	$ 6,063	$ 5,758
Amounts reclassified from AOCI to:
Net realized investment gains (losses)		$ (14)	$ 7	$ 15	32	$ (24)	$ (2)	$ 10	(13)	40	(29)	(26)
Net investment income		96	99	101	122	117	94	98	99	418	408	423
Interest expense		(24)	(24)	(25)	(24)	(25)	(26)	(25)	(26)	(97)	(102)	(101)
Total (provision) benefit for income taxes		(104)	$ (105)	$ 3	(55)	(74)	$ (1)	$ (55)	(6)	(261)	(136)	(375)
Ending balance		6,839				6,504				6,839	6,504	6,063
Net Unrealized Gains (Losses) on Investments with no Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					171				260	171	260	367
Reclassification of stranded tax effects (see Note 1)										38
Other comprehensive income (loss) before reclassifications										128	(71)	(93)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax										(64)	(18)	(14)
Net current period other comprehensive income (loss)										64	(89)	(107)
Ending balance		273				171				273	171	260
Net Unrealized Gains (Losses) on Investments with no Other-Than-Temporary Impairment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)										(71)	(23)	(11)
Net investment income										(27)	(3)	(9)
Interest expense										0	0	0
Total before tax										(98)	(26)	(20)
Total (provision) benefit for income taxes										34	8	6
Net Unrealized Gains (Losses) on Investments with Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					10				(15)	10	(15)	4
Reclassification of stranded tax effects (see Note 1)										21
Other comprehensive income (loss) before reclassifications										69	(9)	(43)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax										20	34	24
Net current period other comprehensive income (loss)										89	25	(19)
Ending balance		120				10				120	10	(15)
Net Unrealized Gains (Losses) on Investments with Other-Than-Temporary Impairment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)										31	52	37
Net investment income										(1)	0	0
Interest expense										0	0	0
Total before tax										30	52	37
Total (provision) benefit for income taxes										(10)	(18)	(13)
Accumulated Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					(39)				(16)	(39)	(16)	(10)
Reclassification of stranded tax effects (see Note 1)										(5)
Other comprehensive income (loss) before reclassifications										15	(23)	(6)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax										0	0	0
Net current period other comprehensive income (loss)										15	(23)	(6)
Ending balance		(29)				(39)				(29)	(39)	(16)
Accumulated Translation Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)										0	0	0
Net investment income										0	0	0
Interest expense										0	0	0
Total before tax										0	0	0
Total (provision) benefit for income taxes										0	0	0
Cash Flow Hedge [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					7				8	7	8	9
Reclassification of stranded tax effects (see Note 1)										2
Other comprehensive income (loss) before reclassifications										0	0	0
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax										(1)	(1)	(1)
Net current period other comprehensive income (loss)										(1)	(1)	(1)
Ending balance		8				7				8	7	8
Cash Flow Hedge [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)										0	0	0
Net investment income										0	0	0
Interest expense										(1)	(1)	(1)
Total before tax										(1)	(1)	(1)
Total (provision) benefit for income taxes										0	0	0
Accumulated Other Comprehensive Income [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					$ 149				$ 237	149	237	370
Reclassification of stranded tax effects (see Note 1)	$ 56									56
Other comprehensive income (loss) before reclassifications										212	(103)	(142)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax										(45)	15	9
Net current period other comprehensive income (loss)										167	(88)	(133)
Ending balance		$ 372				$ 149				372	149	237
Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)										(40)	29	26
Net investment income										(28)	(3)	(9)
Interest expense										(1)	(1)	(1)
Total before tax										(69)	25	16
Total (provision) benefit for income taxes										$ 24	$ (10)	$ (7)