Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net unrealized appreciation, securities pre-tax:
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	$ 98	$ 162	$ 149	$ 177
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(3)	(30)	(19)	(54)
Net unrealized appreciation (depreciation), securities pre-tax	95	132	130	123
Net unrealized appreciation (depreciation) derivatives pre-tax	6	(7)	0	(15)
Net translation of foreign currencies pre-tax	(45)	44	(2)	97
Postretirement benefits liability adjustment pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	12	6	24	11
Settlement adjustment pre-tax			6
Net change due to valuation update pre-tax	24	3	24	3
Net postretirement benefits liability adjustment pre-tax	36	9	54	14
Net unrealized appreciation, securities tax:
Net unrealized appreciation (depreciation) on securities arising during the period tax	(32)	(55)	(48)	(60)
Reclasification adjustment for (gains) losses included in shareholders' net income tax	1	10	6	18
Net unrealized appreciation (depreciation), securities tax	(31)	(45)	(42)	(42)
Net unrealized appreciation (depreciation) derivatives tax	(1)	2	0	5
Net translation of foreign currencies tax	2	(4)	(6)	(9)
Postretirement benefits liability adjustment tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax	(3)	(3)	(8)	(4)
Reclassification adjustment for settlement tax			(2)
Net change due to valuation update tax	(8)	(1)	(8)	(1)
Net postretirement benefits liability adjustment tax	(11)	(4)	(18)	(5)
Net realized appreciation, securities after-tax:
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	66	107	101	117
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(2)	(20)	(13)	(36)
Net unrealized appreciation (depreciation), securities after-tax	64	87	88	81
Net unrealized appreciation (depreciation), derivatives after-tax	5	(5)	0	(10)
Net translation of foreign currencies after-tax	(43)	40	(8)	88
Postretirement benefits liability adjustment after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	9	3	16	7
Reclassification adjustment for settlement after-tax			4
Net change due to valuation update after-tax	16	2	16	2
Net postretirement benefits liability adjustment after-tax	$ 25	$ 5	$ 36	$ 9