Derivative Instruments and Hedging Activities - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 CAD
Foreign Currency Derivatives [Member] | Principal [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD					CAD 370,000,000
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | Long-term other assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency derivatives, Assets		$ 63	$ 28
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | Current Other Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign currency derivatives, Assets		15
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | October 31, 2016 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD					70,000,000
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | October 31, 2017 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD					150,000,000
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | October 31, 2018 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD					CAD 150,000,000
Forward Starting Interest Rate Swap [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Deferred losses for previously terminated swaps recorded as interest expense		$ 3
Forward Starting Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	$ 175
Cash received (paid) to settle hedges	$ 36
Maximum term of cash flow hedges		10 years
Deferred losses, net of taxes, related to cash flow hedges included in accumulated other comprehensive income		$ 43	50
Treasury rate locks [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Deferred losses scheduled to be reclassified out of accumulated other comprehensive into interest expense over next 12 months, pre-tax		11
Interest Rate Swaps [Member] | Fair Value Hedge [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Increase in carrying value of debt instruments from fair value hedge accounting for interest rate swaps		23	45
Benefits (losses) to interest expense associated with the amortization of our terminated interest rate swaps		8	$ 14	$ 20
Interest Rate Swaps [Member] | Fair Value Hedge [Member] | Early Extinguishment of Debt [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Benefits (losses) to interest expense associated with the amortization of our terminated interest rate swaps		$ 14