Derivative Instruments and Hedging Activities - Impact of Periodic Settlements of Active Swap Agreements and Impact of Terminated Swap Agreements on Results of Operations (Detail) (Interest Expense [Member], Fair Value Hedge [Member], Interest Rate Swaps [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Expense [Member] | Fair Value Hedge [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Periodic settlements of active swap agreements			$ 8
Terminated swap agreements	14	20	22
Total	$ 14	$ 20	$ 30