Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), beginning			$ (936)
Shareholders' other comprehensive income (loss)	$ (90)	$ (146)	(279)	$ 101
Accumulated other comprehensive income (loss), ending	(1,215)		(1,215)
Realized investment (gains) losses	(10)	(23)	(104)	(130)
Other operating expenses	2,171	2,034	6,587	6,010
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, beginning	733	1,017	955	733
Other comprehensive income (loss) before reclassifications, pre-tax	(37)	(85)	(226)	228
Reclassification adjustment, pre-tax	29	1	(4)	(28)
Other comprehensive income (loss), pre-tax	(8)	(84)	(230)	200
Accumulated other comprehensive income (loss), before tax, ending	725	933	725	933
Accumulated other comprehensive income/loss tax (expense) benefit, beginning	(259)	(351)	(335)	(256)
Other comprehensive income (loss), securities, before reclassifications, tax (expense) benefit	26	35	90	(70)
Reclassification adjustment, securities, tax (expense) benefit	(10)	0	2	10
Other comprehensive income (loss), tax (expense) benefit	16	35	92	(60)
Accumulated other comprehensive income/loss tax (expense) benefit, ending	(243)	(316)	(243)	(316)
Accumulated other comprehensive income (loss), beginning	474	666	620	477
Other comprehensive income (loss) before reclassifications, after-tax	(11)	(50)	(136)	158
Reclassification adjustment, after-tax	19	1	(2)	(18)
Shareholders' other comprehensive income (loss)	8	(49)	(138)	140
Accumulated other comprehensive income (loss), ending	482	617	482	617
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Realized investment (gains) losses	29	1	(4)	(28)
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, beginning	7	(29)	(12)	(29)
Other comprehensive income (loss) before reclassifications, pre-tax			11
Reclassification adjustment, pre-tax			12
Other comprehensive income (loss), pre-tax	4	9	23	9
Accumulated other comprehensive income (loss), before tax, ending	11	(20)	11	(20)
Accumulated other comprehensive income/loss tax (expense) benefit, beginning	(3)	10	4	10
Other comprehensive income (loss), derivatives, before reclassifications, tax (expense) benefit			(4)
Reclassification adjustment, derivatives, tax (expense) benefit			(4)
Other comprehensive income (loss), tax (expense) benefit	(1)	(3)	(8)	(3)
Accumulated other comprehensive income/loss tax (expense) benefit, ending	(4)	7	(4)	7
Accumulated other comprehensive income (loss), beginning	4	(19)	(8)	(19)
Other comprehensive income (loss) before reclassifications, after-tax			7
Reclassification adjustment, after-tax			8
Shareholders' other comprehensive income (loss)	3	6	15	6
Accumulated other comprehensive income (loss), ending	7	(13)	7	(13)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses			12
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, beginning	(165)	129	(71)	91
Other comprehensive income (loss), pre-tax	(113)	(128)	(207)	(90)
Accumulated other comprehensive income (loss), before tax, ending	(278)	1	(278)	1
Accumulated other comprehensive income/loss tax (expense) benefit, beginning	17	(12)	9	(9)
Other comprehensive income (loss), tax (expense) benefit	1	15	9	12
Accumulated other comprehensive income/loss tax (expense) benefit, ending	18	3	18	3
Accumulated other comprehensive income (loss), beginning	(148)	117	(62)	82
Shareholders' other comprehensive income (loss)	(112)	(113)	(198)	(78)
Accumulated other comprehensive income (loss), ending	(260)	4	(260)	4
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income (loss), before tax, beginning	(2,240)	(1,594)	(2,286)	(1,630)
Other comprehensive income (loss) before reclassifications, pre-tax		1	12	3
Reclassification adjustment, pre-tax	16	13	50	47
Other comprehensive income (loss), pre-tax		14	62	50
Accumulated other comprehensive income (loss), before tax, ending	(2,224)	(1,580)	(2,224)	(1,580)
Accumulated other comprehensive income/loss tax (expense) benefit, beginning	785	557	800	570
Other comprehensive income (loss), postretirement benefits, before reclassifications, tax (expense) benefit		0	(3)	(1)
Reclassification adjustment, postretirement benefits, tax (expense) benefit	(5)	(4)	(17)	(16)
Other comprehensive income (loss), tax (expense) benefit		(4)	(20)	(17)
Accumulated other comprehensive income/loss tax (expense) benefit, ending	780	553	780	553
Accumulated other comprehensive income (loss), beginning	(1,455)	(1,037)	(1,486)	(1,060)
Other comprehensive income (loss) before reclassifications, after-tax		1	9	2
Reclassification adjustment, after-tax	11	9	33	31
Shareholders' other comprehensive income (loss)		10	42	33
Accumulated other comprehensive income (loss), ending	(1,444)	(1,027)	(1,444)	(1,027)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Other operating expenses	16	13	50	47
Accumulated Defined Benefit Plans Adjustment Net Prior Service Cost Credit [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustment, pre-tax	16	13	50	41
Reclassification adjustment, postretirement benefits, tax (expense) benefit	(5)	(4)	(17)	(14)
Reclassification adjustment, after-tax	11	9	33	27
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	$ 16	$ 13	$ 50	41
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