Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net loss arising during the period, income tax expense (benefit)	$ (14)	$ (22)	$ (3)
Amortization of net loss included in net income, income tax expense	5	4	8
Prior service credit arising during the period, income tax expense	0	4	0
Unrealized holding gain (loss) arising during the period, income tax expense (benefit)	(7)	37	36
Reclassification adjustments included in net income, income tax benefit	$ (25)	$ (96)	$ (124)