Shareholders' Equity - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 370	$ 264	$ 370	$ 160
Other comprehensive income (loss) before reclassifications	(136)	61	(125)	164
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	(9)	(8)	7	(6)
Interest expense	(26)	(20)	(51)	(40)
Total (provision) benefit for income taxes	(112)	(59)	(177)	(86)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	5	7	(5)	9
Net current period other comprehensive income (loss)	(131)	68	(131)	172
Balance at end of period	239	332	239	332
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from AOCI to:
Net realized investment gains (losses)	9	10	(7)	13
Interest expense	0	0	(1)	0
Total before tax	9	10	(8)	13
Total (provision) benefit for income taxes	(4)	(3)	2	(5)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	5	7	(6)	8
Net Unrealized Gains (Losses) on Investments with no Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	372	271	367	178
Other comprehensive income (loss) before reclassifications	(136)	75	(118)	169
Amounts reclassified from AOCI to:
Net current period other comprehensive income (loss)	(136)	74	(131)	167
Balance at end of period	236	345	236	345
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)	1	(2)	(19)	(4)
Interest expense	0	0	0	0
Total before tax	1	(2)	(19)	(4)
Total (provision) benefit for income taxes	(1)	1	6	2
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	0	(1)	(13)	(2)
Net Unrealized Gains (Losses) on Investments with Other-Than-Temporary Impairment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	5	(13)	4	(24)
Other comprehensive income (loss) before reclassifications	(6)	(17)	(8)	(9)
Amounts reclassified from AOCI to:
Net current period other comprehensive income (loss)	(1)	(9)	0	2
Balance at end of period	4	(22)	4	(22)
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)	8	12	12	17
Interest expense	0	0	0	0
Total before tax	8	12	12	17
Total (provision) benefit for income taxes	(3)	(4)	(4)	(6)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	5	8	8	11
Accumulated Translation Adjustment [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	(15)	(2)	(10)	(3)
Other comprehensive income (loss) before reclassifications	6	3	1	4
Amounts reclassified from AOCI to:
Net current period other comprehensive income (loss)	6	3	1	4
Balance at end of period	(9)	1	(9)	1
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
Interest expense	0	0	0	0
Total before tax	0	0	0	0
Total (provision) benefit for income taxes	0	0	0	0
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	0	0	0	0
Cash Flow Hedge [Member]
Changes in Accumulated Other Comprehensive Income [Roll Forward]
Balance at beginning of period	8	8	9	9
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI to:
Net current period other comprehensive income (loss)	0	0	(1)	(1)
Balance at end of period	8	8	8	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
Interest expense	0		(1)	0
Total before tax	0	0	(1)	0
Total (provision) benefit for income taxes	0	0	0	(1)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $(21), $5 and $(7)	$ 0	$ 0	$ (1)	$ (1)