Derivative Instruments and Hedging Activities - Additional Information (Detail) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 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]
Notional amount of derivatives	$ 73			$ 73		$ 28
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member] | Current Accrued Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives	1			1
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	45			$ 45		50
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				25		$ 45
Benefits (losses) to interest expense associated with the amortization of our terminated interest rate swaps	2	$ 3		6	$ 11
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
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			$ 11
October 31, 2016 [Member] | Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD							70,000,000
October 31, 2017 [Member] | Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD							150,000,000
October 31, 2018 [Member] | Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of derivatives | CAD							CAD 150,000,000