Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Net unrealized appreciation, securities pre-tax:
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	$ (36)	$ 51
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(70)	(16)
Net unrealized appreciation (depreciation), securities pre-tax	(106)	35
Net unrealized appreciation (depreciation) derivatives pre-tax	4	(6)
Net translation of foreign currencies pre-tax	(69)	43
Postretirement benefits liability adjustment pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	17	12
Reclassification adjustment for curtailment or settlement (other operating expenses)	(19)	6
Total reclassification adjustments to shareholders' net income (other operating expenses)	(2)
Net change due to valuation update and plan amedments	63
Net postretirement benefits liability adjustment pre-tax	61	18
Net unrealized appreciation, securities tax (expense) benefit:
Net unrealized appreciation (depreciation) on securities arising during the period tax (expense) benefit	12	(16)
Reclassification adjustment for (gains) losses included in shareholders' net income tax (expense) benefit	24	5
Net unrealized appreciation (depreciation), securities tax (expense) benefit	36	(11)
Net unrealized appreciation (depreciation) derivatives tax (expense) benefit	(1)	1
Net translation of foreign currencies tax (expense) benefit	11	(8)
Postretirement benefits liability adjustment tax (expense) benefit:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax (expense) benefit	(6)	(5)
Reclassification adjustment for curtailment or settlement (other operating expenses)	7	(2)
Total reclassification adjustments to shareholders' net income (other operating expenses)	1
Net change due to valuation update and plan amedments	(22)
Net postretirement benefits liability adjustment tax (expense) benefit	(21)	(7)
Net realized appreciation, securities after-tax:
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	(24)	35
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(46)	(11)
Net unrealized appreciation (depreciation), securities after-tax	(70)	24
Net unrealized appreciation (depreciation), derivatives after-tax	3	(5)
Net translation of foreign currencies after-tax	(58)	35
Postretirement benefits liability adjustment after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	11	7
Reclassification adjustment for curtailment or settlement (other operating expenses)	(12)	4
Total reclassification adjustments to shareholders' net income (other operating expenses)	(1)
Net change due to valuation update and plan amedments	41
Net postretirement benefits liability adjustment after-tax	$ 40	$ 11