Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), January 1,	$ (520)
Shareholders' other comprehensive income (loss)	(415)	151	116
Accumulated other comprehensive income (loss), December 31,	(936)	(520)
Other realized investment (gains) losses	(190)	(224)	(55)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, January 1,	733	1,352	1,133
Other comprehensive income (loss) before reclassifications, pre-tax	249	(498)	271
Reclassification adjustment, pre-tax	(27)	(121)	(52)
Other comprehensive income (loss), pre-tax	222	(619)	219
Accumulated other comprehensive income (loss), before tax, December 31,	955	733	1,352
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, January 1,	(256)	(465)	(393)
Other comprehensive income (loss), securities, before reclassifications, tax (expense) benefit	(89)	166	(90)
Reclassification adjustment, securities, tax (expense) benefit	10	43	18
Other comprehensive income (loss), tax (expense) benefit	(79)	209	(72)
Other comprehensive income (loss) before reclassifications, after-tax	160	(332)	181
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, December 31,	(335)	(256)	(465)
Accumulated other comprehensive income (loss), January 1,	477	887	740
Reclassification adjustment, after-tax	(17)	(78)	(34)
Shareholders' other comprehensive income (loss)	143	(410)	147
Accumulated other comprehensive income (loss), December 31,	620	477	887
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other realized investment (gains) losses	(27)	(121)	(52)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, January 1,	(29)	(43)	(36)
Other comprehensive income (loss), pre-tax	17	14	(7)
Accumulated other comprehensive income (loss), before tax, December 31,	(12)	(29)	(43)
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, January 1,	10	15	13
Other comprehensive income (loss), tax (expense) benefit	(6)	(5)	2
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, December 31,	4	10	15
Accumulated other comprehensive income (loss), January 1,	(19)	(28)	(23)
Shareholders' other comprehensive income (loss)	11	9	(5)
Accumulated other comprehensive income (loss), December 31,	(8)	(19)	(28)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, January 1,	91	91	13
Other comprehensive income (loss), pre-tax	(162)	0	78
Accumulated other comprehensive income (loss), before tax, December 31,	(71)	91	91
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, January 1,	(9)	(22)	(10)
Other comprehensive income (loss), tax (expense) benefit	18	13	(12)
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, December 31,	9	(9)	(22)
Accumulated other comprehensive income (loss), January 1,	82	69	3
Shareholders' other comprehensive income (loss)	(144)	13	66
Accumulated other comprehensive income (loss), December 31,	(62)	82	69
Accumulated Defined Benefit Plans Adjustment Net Prior Service Cost Credit [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax	54	70	52
Reclassification adjustment, postretirement benefits, tax (expense) benefit	(18)	(25)	(18)
Reclassification adjustment, after-tax	36	45	34
Accumulated Defined Benefit Plans Adjustment Net Prior Service Cost Credit [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses	54	70	52
Accumulated Defined Benefit Plans Adjustment Curtailment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax		(19)
Reclassification adjustment, postretirement benefits, tax (expense) benefit		7
Reclassification adjustment, after-tax		(12)
Accumulated Defined Benefit Plans Adjustment Curtailment [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses		(19)
Accumulated Defined Benefit Plans Adjustment Settlement [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax	6
Reclassification adjustment, postretirement benefits, tax (expense) benefit	(2)
Reclassification adjustment, after-tax	4
Accumulated Defined Benefit Plans Adjustment Settlement [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses	6
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, January 1,	(1,630)	(2,460)	(2,331)
Other comprehensive income (loss) before reclassifications, pre-tax	(716)	779	(181)
Reclassification adjustment, pre-tax	60	51
Other comprehensive income (loss), pre-tax	(656)	830	(129)
Accumulated other comprehensive income (loss), before tax, December 31,	(2,286)	(1,630)	(2,460)
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, January 1,	570	861	824
Reclassification adjustment, postretirement benefits, tax (expense) benefit	(20)	(18)
Other comprehensive income (loss), postretirement benefits, before reclassifications, tax (expense) benefit	250	(273)	55
Other comprehensive income (loss), tax (expense) benefit	230	(291)	37
Other comprehensive income (loss) before reclassifications, after-tax	(466)	506	(126)
Accumulated Other Comprehensive Income/Loss Tax (Expense) Benefit, December 31,	800	570	861
Accumulated other comprehensive income (loss), January 1,	(1,060)	(1,599)	(1,507)
Reclassification adjustment, after-tax	40	33
Shareholders' other comprehensive income (loss)	(426)	539	(92)
Accumulated other comprehensive income (loss), December 31,	(1,486)	(1,060)	(1,599)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses	$ 60	$ 51