Derivative Instruments and Other Hedging Activities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative Assets - Notional Amount	$ 3,759,695	$ 2,311,612
Derivative Liabilities - Notional Amount	2,994,815	1,991,559
Cash posted as variation margin for derivatives	106,500	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	2,959,695	1,903,112
Derivative Liabilities - Notional Amount	2,886,315	1,991,559
Not Designated as Hedging Instruments | Interest rate contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	2,259,248	701,257
Derivative Liabilities - Notional Amount	142,425	919,653
Not Designated as Hedging Instruments | Customer swaps - upstream
Derivative [Line Items]
Derivative Assets - Notional Amount	142,425	919,653
Derivative Liabilities - Notional Amount	2,259,248	701,257
Not Designated as Hedging Instruments | Other contracts
Derivative [Line Items]
Derivative Assets - Notional Amount	74,085	50,527
Derivative Liabilities - Notional Amount	145,443	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	144,368	1,140
Derivative Liabilities - Notional Amount	211,049	143,179
Not Designated as Hedging Instruments | Written and purchased options
Derivative [Line Items]
Derivative Assets - Notional Amount	339,569	229,333
Derivative Liabilities - Notional Amount	$ 128,150	$ 140,645