Derivative Instruments - Additional Information (Detail) CAD in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 CAD	Jun. 30, 2017 USD ($)
Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract notional amount					$ 170,000,000.0
Interest expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-tax loss reclassified into interest expense		$ 12,400,000
Forward-starting interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract notional amount			$ 2,500,000,000
Cross-currency rate swap maturity date			Mar. 31, 2021
Forward-starting interest rate swaps | Interest expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net unrealized loss remaining in AOCI			$ 84,600,000
Cross Currency Interest Rate Contract
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash received on hedge	$ 763,500,000
Net unrealized gains as of termination date	$ 533,400,000
Cross Currency Interest Rate Contract | Fixed Income Interest Rate
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract notional amount						CAD 6,753.5	$ 5,000,000,000
Cross Currency Interest Rate Contract | Fixed Income Interest Rate | Hedge Funds
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract notional amount				€ 1,107,800,000.0	$ 1,200,000,000
Cross Currency Interest Rate Contract | United States Dollar
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Foreign currency forward contract notional amount							$ 5,000,000,000
Interest Rate Swaps Outstanding As Of December 31, 2016 | Forward-starting interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Type of interest rate paid on swap			fixed