Derivative Financial Instruments - Notional Values (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional values	$ 7,200,000
Interest rate swaps
Derivatives, Fair Value [Line Items]
Notional values	7,201,245	$ 5,459,075
Interest rate swaps | Trading
Derivatives, Fair Value [Line Items]
Notional values	1,577,978	987,577
Interest rate swaps | Cash Flow Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	1,312,573	1,408,649
Interest rate swaps | Fair Value Hedges | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Notional values	$ 4,310,694	$ 3,062,849