Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net unrealized appreciation, securities pre-tax:
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	$ (498)	$ 271	$ 366
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(121)	(52)	(49)
Net unrealized appreciation (depreciation), securities pre-tax	(619)	219	317
Net unrealized appreciation (depreciation) derivatives pre-tax	14	(7)	1
Net translation of foreign currencies pre-tax	0	78	(21)
Postretirement benefits liability adjustment pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	70	52	22
Reclassification adjustment for curtailment or settlement (other operating expenses)	(19)
Total reclassification adjustments to shareholders' net income (other operating expenses)	51
Net change arising from assumption and plan changes and experience	779	(181)	(580)
Net postretirement benefits liability adjustment pre-tax	830	(129)	(558)
Net unrealized appreciation, securities tax (expense) benefit:
Net unrealized appreciation (depreciation) on securities arising during the period tax (expense) benefit	166	(90)	(127)
Reclasification adjustment for (gains) losses included in shareholders' net income tax (expense) benefit	43	18	18
Net unrealized appreciation (depreciation), securities tax (expense) benefit	209	(72)	(109)
Net unrealized appreciation (depreciation) derivatives tax (expense) benefit	(5)	2	0
Net translation of foreign currencies tax (expense) benefit	13	(12)	(1)
Postretirement benefits liability adjustment tax (expense) benefit:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax (expense) benefit	(25)	(18)	(7)
Reclassification adjustment for curtailment or settlement (other operating expenses)	7
Total reclassification adjustments to shareholders' net income (other operating expenses)	(18)
Net change arising from assumption and plan changes and experience tax (expense) benefit	(273)	55	205
Net postretirement benefits liability adjustment tax (expense) benefit	(291)	37	198
Net realized appreciation, securities after-tax:
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	(332)	181	239
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(78)	(34)	(31)
Net unrealized appreciation (depreciation), securities after-tax	(410)	147	208
Net unrealized appreciation (depreciation), derivatives after-tax	9	(5)	1
Net translation of foreign currencies after-tax	13	66	(22)
Postretirement benefits liability adjustment after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	45	34	15
Reclassification adjustment for curtailment or settlement (other operating expenses)	(12)
Total reclassification adjustments to shareholders' net income (other operating expenses)	33
Net change arising from assumption and plan changes and experience after-tax	506	(126)	(375)
Net postretirement benefits liability adjustment after-tax	$ 539	$ (92)	$ (360)