Shareholders' Equity - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 6,504
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	32	$ (13)
Net investment income	122	99
Interest expense	(24)	(26)
Tax (provision) benefit	(55)	(6)
Ending balance	6,637
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
Other comprehensive income (loss) before reclassifications	44	95
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	(45)	(5)
Net current period other comprehensive income (loss)	(1)	90
Ending balance	170	350
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)	(41)	(4)
Net investment income	(28)	(3)
Interest expense	0	0
Total before tax	(69)	(7)
Tax (provision) benefit	24	2
Net Unrealized Gains (Losses) on Investments with Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	10	(15)
Other comprehensive income (loss) before reclassifications	50	(17)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	6	11
Net current period other comprehensive income (loss)	56	(6)
Ending balance	66	(21)
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)	9	17
Net investment income	0	0
Interest expense	0	0
Total before tax	9	17
Tax (provision) benefit	(3)	(6)
Cumulative Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(39)	(16)
Other comprehensive income (loss) before reclassifications	2	(2)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	0	0
Net current period other comprehensive income (loss)	2	(2)
Ending balance	(37)	(18)
Cumulative Translation Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	0	0
Net investment income	0	0
Interest expense	0	0
Total before tax	0	0
Tax (provision) benefit	0	0
Cash Flow Hedge [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	7	8
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	0	0
Net current period other comprehensive income (loss)	0	0
Ending balance	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
Net investment income	0	0
Interest expense	0	0
Total before tax	0	0
Tax (provision) benefit	0	0
Total Accumulated Other Comprehensive Income [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	149	237
Other comprehensive income (loss) before reclassifications	96	76
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	(39)	6
Net current period other comprehensive income (loss)	57	82
Ending balance	206	319
Total Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(32)	13
Net investment income	(28)	(3)
Interest expense	0	0
Total before tax	(60)	10
Tax (provision) benefit	$ 21	$ (4)