Activity Related to Fully Effective Interest Rate Swaps Designated as Fair Value Hedges (Detail) (Fair Value Hedging, USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Issued
Derivative [Line Items]
Interest rate swap agreements outstanding	$ 0	$ 200
Issued | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	100	[1]
Issued | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	100	[1]
Terminated
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Terminated | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Terminated | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Nondesignated
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Nondesignated | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Nondesignated | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	$ 0	$ 0

[1] Fixed-to-floating interest rate swaps were effective when issued and were terminated in the third quarter of 2011.