Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net unrealized appreciation, securities pre-tax:
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	$ 134	$ 115	$ 283	$ 292
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(9)	23	(28)	(31)
Net unrealized appreciation (depreciation), securities pre-tax	125	138	255	261
Net unrealized appreciation (depreciation) derivatives pre-tax	(5)	20	(5)	5
Net translation of foreign currencies pre-tax	39	(111)	37	(14)
Postretirement benefits liability adjustment pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	12	6	36	17
Settlement adjustment pre-tax			6
Net change due to valuation update pre-tax			24	3
Net postretirement benefits liability adjustment pre-tax	12	6	66	20
Net unrealized appreciation, securities tax:
Net unrealized appreciation (depreciation) on securities arising during the period tax	(45)	(39)	(94)	(99)
Reclasification adjustment for (gains) losses included in shareholders' net income tax	3	(8)	10	10
Net unrealized appreciation (depreciation), securities tax	(42)	(47)	(84)	(89)
Net unrealized appreciation (depreciation) derivatives tax	1	(7)	1	(2)
Net translation of foreign currencies tax	(8)	16	(14)	7
Postretirement benefits liability adjustment tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax	(4)	(2)	(12)	(6)
Reclassification adjustment for settlement tax			(2)
Net change due to valuation update tax			(8)	(1)
Net postretirement benefits liability adjustment tax	(4)	(2)	(22)	(7)
Net realized appreciation, securities after-tax:
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	89	76	189	193
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(6)	15	(18)	(21)
Net unrealized appreciation (depreciation), securities after-tax	83	91	171	172
Net unrealized appreciation (depreciation), derivatives after-tax	(4)	13	(4)	3
Net translation of foreign currencies after-tax	31	(95)	23	(7)
Postretirement benefits liability adjustment after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	8	4	24	11
Reclassification adjustment for settlement after-tax			4
Net change due to valuation update after-tax			16	2
Net postretirement benefits liability adjustment after-tax	$ 8	$ 4	$ 44	$ 13