Commitments - Other Commitments (Detail) $ in Billions	12 Months Ended
	Dec. 31, 2015 USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]
Aggregate future payments	$ 10.1
Aggregate future payments expected to be paid in 2016	1.9
Aggregate future payments expected to be paid in 2017	1.7
Aggregate future payments expected to be paid in 2018	1.3
Aggregate future payments expected to be paid in 2019	1.2
Aggregate future payments expected to be paid in 2020	1.1
Aggregate future payments expected to be paid thereafter	$ 2.9
Maximum [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Other commitments, expiration date	Dec. 31, 2036