Derivatives Designated as Hedging Instruments (Parenthetical) (Detail) (Interest Rate Swaps, USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Interest Rate Swaps
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate derivative asset	$ 60

The increase (decrease) during the period in the carrying value of derivative instruments reported as liabilities that are due to be disposed of within one year (or the normal operating cycle, if longer).

No definition available.

Name:	us-gaap_IncreaseDecreaseInDerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration