Debt (Principal Payments Due Under Medium-Term Note Obligations Based On Contractual Maturity) (Detail) (USD $) In Millions, unless otherwise specified			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Medium-Term Notes [Member]
Debt Maturities [Line Items]
2013			$ 41
2014			47
2015			255
2016			128
2017			53
Thereafter			1,847
Total expected principal payments	723	901	2,371	[1]
Less discount and other adjustments			773	[2]
Total			1,598
Discounts	1	1	759
Fair value adjustments			23
Accrued interest			$ 9

[1] Foreign currency denominated MTN's are presented in U.S. dollars. Amounts reflect principal due at maturity for notes issued at a discount or premium.

[2] Includes discounts of $759 million and fair value adjustments of $23 million, net of accrued interest of $9 million.