Calculation of Earnings Per Share and the Reconciliation of Earnings Per Share to Earnings Per Diluted Share (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Preferred dividends	$ 203	$ 250	$ 226
Preferred stock Series G
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Preferred dividends			14
Reduction to preferred dividends due to the conversion of a portion of Series G preferred shares			$ 35