Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net unrealized appreciation (depreciation), securities, pre-tax:
Net unrealized appreciation (depreciation) on securities arising during the period pre-tax	$ (4)	$ 134	$ (424)	$ 283
Reclassification adjustment for (gains) losses included in shareholders' net income pre-tax	(16)	(9)	(109)	(28)
Net unrealized appreciation (depreciation), securities pre-tax	(20)	125	(533)	255
Net unrealized appreciation (depreciation) derivatives pre-tax	(4)	(5)	10	(5)
Net translation of foreign currencies pre-tax	68	39	(24)	37
Postretirement benefits liability adjustment, pre-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs pre-tax	19	12	53	36
Reclassification adjustment for curtailment or settlement (other operating expenses)			(19)	6
Total reclassification adjustments to shareholders' net income (other operating expenses)			34	42
Net change due to valuation update and plan amedments			79	24
Net postretirement benefits liability adjustment pre-tax	19	12	113	66
Net unrealized appreciation, securities, tax (expense) benefit:
Net unrealized appreciation (depreciation) on securities arising during the period tax (expense) benefit	0	(45)	142	(94)
Reclassification adjustment for (gains) losses included in shareholders' net income tax (expense) benefit	6	3	38	10
Net unrealized appreciation (depreciation), securities tax (expense) benefit	6	(42)	180	(84)
Net unrealized appreciation (depreciation) derivatives tax (expense) benefit	2	1	(3)	1
Net translation of foreign currencies tax (expense) benefit	(9)	(8)	9	(14)
Postretirement benefits liability adjustment, tax (expense) benefit:
Reclassification adjustment for amortization of net losses from past experience and prior service costs tax (expense) benefit	(7)	(4)	(19)	(12)
Reclassification adjustment for curtailment or settlement (other operating expenses)			7	(2)
Total reclassification adjustments to shareholders' net income (other operating expenses)			(12)	(14)
Net change due to valuation update and plan amedments			(28)	(8)
Net postretirement benefits liability adjustment tax (expense) benefit	(7)	(4)	(40)	(22)
Net realized appreciation (depreciation), securities after-tax:
Net unrealized appreciation (depreciation) on securities arising during the period after-tax	(4)	89	(282)	189
Reclassification adjustment for (gains) losses included in shareholders' net income after-tax	(10)	(6)	(71)	(18)
Net unrealized appreciation (depreciation), securities after-tax	(14)	83	(353)	171
Net unrealized appreciation (depreciation), derivatives after-tax	(2)	(4)	7	(4)
Net translation of foreign currencies after-tax	59	31	(15)	23
Postretirement benefits liability adjustment, after-tax:
Reclassification adjustment for amortization of net losses from past experience and prior service costs after-tax	12	8	34	24
Reclassification adjustment for curtailment or settlement (other operating expenses)			(12)	4
Total reclassification adjustments to shareholders' net income (other operating expenses)			22	28
Net change due to valuation update and plan amedments			51	16
Net postretirement benefits liability adjustment after-tax	$ 12	$ 8	$ 73	$ 44