Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net unrealized appreciation, securities pre-tax:
Implementation effect of updated guidance on other-than-temporary impairments pre-tax		$ 0
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	51	15
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(16)	(24)
Net unrealized appreciation (depreciation), securities pre-tax	35	(9)
Net unrealized appreciation (depreciation) derivatives pre-tax	(6)	(8)
Net translation of foreign currencies pre-tax	43	53
Postretirement benefits liability adjustment pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	12	5
Settlement adjustment pre-tax	6
Net postretirement benefits liability adjustment pre-tax	18
Net unrealized appreciation, securities tax:
Implementation effect of updated guidance on other-than-temporary impariments tax		0
Net unrealized appreciation (depreciation) on securities arising during the period tax	(16)	(5)
Reclasification adjustment for (gains) losses included in shareholders' net income tax	5	8
Net unrealized appreciation (depreciation), securities tax	(11)	3
Net unrealized appreciation (depreciation) derivatives tax	1	3
Net translation of foreign currencies tax	(8)	(5)
Postretirement benefits liability adjustment tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax	(5)	(1)
Reclassification adjustment for settlement tax	(2)
Net postretirement benefits liability adjustment tax	(7)
Net realized appreciation, securities after-tax:
Implementation effect of updated guidance on other-than-temporary impariments after-tax		0
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	35	10
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(11)	(16)
Net unrealized appreciation (depreciation), securities after-tax	24	(6)
Net unrealized appreciation (depreciation), derivatives after-tax	(5)	(5)
Net translation of foreign currencies after-tax	35	48
Postretirement benefits liability adjustment after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	7
Reclassification adjustment for settlement after-tax	4
Net postretirement benefits liability adjustment after-tax	$ 11	$ 4