Activity Related to Fully Effective Interest Rate Swaps Designated as Fair Value Hedges (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Fair Value Hedging | Issued
Derivative [Line Items]
Interest rate swap agreements outstanding	$ 0	$ 200
Fair Value Hedging | Issued | Third Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Fair Value Hedging | Issued | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	100	[1]
Fair Value Hedging | Issued | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	100	[1]
Fair Value Hedging | Terminated
Derivative [Line Items]
Interest rate swap agreements outstanding	0	464
Fair Value Hedging | Terminated | Third Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	464	[2]
Fair Value Hedging | Terminated | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Fair Value Hedging | Terminated | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Fair Value Hedging | Nondesignated
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Fair Value Hedging | Nondesignated | Third Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0	[2]
Fair Value Hedging | Nondesignated | Second Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Fair Value Hedging | Nondesignated | First Quarter
Derivative [Line Items]
Interest rate swap agreements outstanding	0	0
Long-term Debt | Fixed To Floating Interest Rate Swap Member
Derivative [Line Items]
Deferred gain recorded in long-term debt		$ 27

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

[2] Terminations of fixed-to-floating interest rate swaps were not in connection with early debt retirements. The resulting $27 million gain was deferred and recorded in Long-term debt and is being amortized as an adjustment of interest expense over the life of the respective underlying debt through June 2014, March 2015 or March 2016.