Derivatives and Hedging Activities and Fair Value Measurement - Currency Values under Significant Currency Positions Pursuant to Currency Derivatives Outstanding (Detail) - Long [Member]	3 Months Ended
	Mar. 31, 2021 CAD ($)
CAD/USD Denominated Notional Contractual Value For 2021 [Member]
Derivative [Line Items]
Notional contractual value	$ 555,000,000
Percentage of forecasted net exposures under contracts	78.00%
Currency exposure hedged, Average Protection rate	1.3334
Currency exposure hedged, Average Obligation rate	1.3520
CAD/USD Denominated Notional Contractual Value For 2022 [Member]
Derivative [Line Items]
Notional contractual value	$ 442,000,000
Percentage of forecasted net exposures under contracts	47.00%
Currency exposure hedged, Average Protection rate	1.3327
Currency exposure hedged, Average Obligation rate	1.3405
CAD/USD Denominated Notional Contractual Value For 2023 [Member]
Derivative [Line Items]
Notional contractual value	$ 66,000,000
Percentage of forecasted net exposures under contracts	7.00%
Currency exposure hedged, Average Protection rate	1.2685
Currency exposure hedged, Average Obligation rate	1.2685