Subsequent Event (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Subsequent Event [Line Items]
Treasury Stock, Value, Acquired, Cost Method	$ (650)
Treasury Stock Acquired, Repurchase Authorization	100
Common Stock
Subsequent Event [Line Items]
Treasury Stock, Value, Acquired, Cost Method	125
Treasury Stock Repurchase Approval	$ 600