Commitments - Other Commitments (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012
Unrecorded Unconditional Purchase Obligation [Line Items]
Aggregate future payments	8,800,000,000
Aggregate future payments expected to be paid in 2013	1,700,000,000
Aggregate future payments expected to be paid in 2014	1,400,000,000
Aggregate future payments expected to be paid in 2015	1,100,000,000
Aggregate future payments expected to be paid in 2016	881,000,000
Aggregate future payments expected to be paid in 2017	772,000,000
Aggregate future payments expected to be paid thereafter	2,900,000,000
Maximum [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Other commitments, expiration date	Dec. 31, 2028