Derivative Instruments and Other Hedging Activities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Assets - Notional Amount	$ 3,513,310	$ 2,311,612
Derivative Liabilities - Notional Amount	2,883,353	1,991,559
Cash posted as variation margin for derivatives	78,400	35,800
Designated as Hedging Instruments
Derivative [Line Items]
Derivative Assets - Notional Amount	800,000	408,500
Derivative Liabilities - Notional Amount	108,500	0
Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	800,000	408,500
Derivative Liabilities - Notional Amount	108,500	0
Not Designated as Hedging Instruments
Derivative [Line Items]
Derivative Assets - Notional Amount	2,713,310	1,903,112
Derivative Liabilities - Notional Amount	2,774,853	1,991,559
Not Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	1,885,919	701,257
Derivative Liabilities - Notional Amount	375,805	919,653
Not Designated as Hedging Instruments | Customer swaps - upstream
Derivative [Line Items]
Derivative Assets - Notional Amount	375,805	919,653
Derivative Liabilities - Notional Amount	1,885,919	701,257
Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	54,568	50,527
Derivative Liabilities - Notional Amount	113,396	85,623
Not Designated as Hedging Instruments | Foreign exchange contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	0	1,202
Derivative Liabilities - Notional Amount	0	1,202
Not Designated as Hedging Instruments | Forward sales contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	46,143	1,140
Derivative Liabilities - Notional Amount	262,566	143,179
Not Designated as Hedging Instruments | Written and purchased options
Derivative [Line Items]
Derivative Assets - Notional Amount	350,875	229,333
Derivative Liabilities - Notional Amount	$ 137,167	$ 140,645