Shareholders' Equity - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance			$ 6,063
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	$ 10	$ (9)	(3)	$ 7
Net investment income	98	98	197	199
Interest expense	(25)	(26)	(51)	(51)
Tax (provision) benefit	(55)	(112)	(61)	(177)
Ending balance	6,250		6,250
Net Unrealized Gains (Losses) on Investments with no Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	350	372	260	367
Other comprehensive income (loss) before reclassifications	84	(136)	179	(118)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	(8)	0	(13)	(13)
Net current period other comprehensive income (loss)	76	(136)	166	(131)
Ending balance	426	236	426	236
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)	(13)	1	(17)	(19)
Net investment income	0		(3)
Interest expense	0	0	0	0
Total before tax	(13)	1	(20)	(19)
Tax (provision) benefit	5	(1)	7	6
Net Unrealized Gains (Losses) on Investments with Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(21)	5	(15)	4
Other comprehensive income (loss) before reclassifications	(6)	(6)	(23)	(8)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	3	5	14	8
Net current period other comprehensive income (loss)	(3)	(1)	(9)	0
Ending balance	(24)	4	(24)	4
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)	4	8	21	12
Net investment income	0		0
Interest expense	0	0	0	0
Total before tax	4	8	21	12
Tax (provision) benefit	(1)	(3)	(7)	(4)
Accumulated Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(18)	(15)	(16)	(10)
Other comprehensive income (loss) before reclassifications	(8)	6	(10)	1
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	0	0	0	0
Net current period other comprehensive income (loss)	(8)	6	(10)	1
Ending balance	(26)	(9)	(26)	(9)
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	0
Net investment income	0		0
Interest expense	0	0	0	0
Total before tax	0	0	0	0
Tax (provision) benefit	0	0	0	0
Cash Flow Hedge [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	8	8	8	9
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	(1)	0	(1)	(1)
Net current period other comprehensive income (loss)	(1)	0	(1)	(1)
Ending balance	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	0
Net investment income	0		0
Interest expense	(1)	0	(1)	(1)
Total before tax	(1)	0	(1)	(1)
Tax (provision) benefit	0	0	0	0
Accumulated Other Comprehensive Income [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	319	370	237	370
Other comprehensive income (loss) before reclassifications	70	(136)	146	(125)
Amounts reclassified from AOCI to:
Total amount reclassified from AOCI, net of tax	(6)	5	0	(6)
Net current period other comprehensive income (loss)	64	(131)	146	(131)
Ending balance	383	239	383	239
Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(9)	9	4	(7)
Net investment income	0		(3)
Interest expense	(1)	0	(1)	(1)
Total before tax	(10)	9	0	(8)
Tax (provision) benefit	$ 4	$ (4)	$ 0	$ 2