Derivatives (Narrative) (Details) Boe in Thousands, MMBTU in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($) warrant	Jun. 30, 2017 hedge	Jun. 30, 2018 USD ($) MMBTU Boe warrant	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) warrant contract
Derivative [Line Items]
Derivative liabilities	$ 114,542,000		$ 114,542,000		$ 74,935,000
Derivative assets	81,456,000		81,456,000		$ 66,146,000
Number of derivative contracts designated as investment hedge | contract					0
Number of investment hedges designated and recorded | hedge		0
Derivative asset, reduction in fair value	54,315,000		54,315,000		$ 29,205,000
Derivative liability, reduction in fair value	31,577,000		31,577,000		48,203,000
Collateral posted	12,889,000		12,889,000		28,796,000
Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	131,326,000		131,326,000		35,811,000
Derivative liabilities	8,647,000		8,647,000		6,799,000
Derivative assets	2,316,000		2,316,000		0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	12,295,137,000		12,295,137,000		10,153,108,000
Derivative liabilities	105,895,000		105,895,000		68,136,000
Derivative assets	79,140,000		79,140,000		66,146,000
Derivatives not designated as hedging instruments | Financial Counterparties
Derivative [Line Items]
Derivative liabilities	2,888		2,888
Derivative assets	0		0
Interest rate swaps | Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	35,811,000		35,811,000		35,811,000
Derivative liabilities	8,647,000		8,647,000		6,799,000
Derivative assets	0		0		0
Interest rate swaps | Derivatives designated as hedging instruments | Fair Value Hedges
Derivative [Line Items]
Notional amount	35,800,000		35,800,000		35,800,000
Derivative liabilities	8,600,000		8,600,000		6,800,000
Foreign exchange forwards | Derivatives designated as hedging instruments
Derivative [Line Items]
Notional amount	95,515,000		95,515,000		0
Derivative liabilities	0		0		0
Derivative assets	2,316,000		2,316,000		0
Foreign exchange forwards | Derivatives designated as hedging instruments | Net investment hedges
Derivative [Line Items]
Notional amount	95,500,000		95,500,000
Derivative assets	2,300,000		2,300,000
Total fair value change in foreign currency translation adjustment with aoci	4,900,000		3,800,000
Gain (loss) recognized in AOCI on net investment hedges (effective portion)				$ (648,000)
(Losses) gains recognized in foreign exchange income (ineffective portion)				$ (2,000,000)
Interest rate swaps and options | Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	11,217,468,000		11,217,468,000		9,333,860,000
Derivative liabilities	91,378,000		91,378,000		57,958,000
Derivative assets	64,225,000		64,225,000		58,633,000
Interest rate swaps and options | Derivatives not designated as hedging instruments | LCH
Derivative [Line Items]
Derivative asset, reduction in fair value	(32,200,000)		(32,200,000)
Derivative liability, reduction in fair value	(2,900,000)		(2,900,000)
Notional amount of derivative assets	1,550,000,000		1,550,000,000
Fair value of interest rate swaps cleared through LCH	241,000		241,000
Interest rate swaps and options | Derivatives not designated as hedging instruments | Financial Counterparties
Derivative [Line Items]
Notional amount of derivative assets	5,610,000,000		5,610,000,000
RPAs | Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	118,024,000		118,024,000		49,033,000
Derivative liabilities	77,000		77,000		8,000
Derivative assets	1,000		$ 1,000		$ 1,000
Weighted average remaining maturity (in years)			6 years 8 months 12 days		6 years
RPAs | Derivatives not designated as hedging instruments | Long
Derivative [Line Items]
Notional amount	105,800,000		$ 105,800,000		$ 35,200,000
Derivative liabilities	77,000		77,000		8,000
Derivative assets	0		0		0
Interest rate derivative exposure	962,000		962,000		419,000
RPAs | Derivatives not designated as hedging instruments | Short
Derivative [Line Items]
Notional amount	12,300,000		12,300,000		13,800,000
Derivative liabilities	0		0		0
Derivative assets	1,000		1,000		1,000
Equity warrants | Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	0		0		0
Derivative liabilities	0		0		0
Derivative assets	$ 1,878,000		$ 1,878,000		$ 1,672,000
Warrant, Public Companies | Derivatives not designated as hedging instruments
Derivative [Line Items]
Number of warrants held | warrant	4		4		4
Warrant, Private Companies | Derivatives not designated as hedging instruments
Derivative [Line Items]
Number of warrants held | warrant	14		14		11
Commodity swaps and options | Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	$ 0		$ 0		$ 0
Derivative liabilities	3,159,000		3,159,000		0
Derivative assets	3,628,000		3,628,000		0
Commodity swaps and options | Derivatives not designated as hedging instruments | Chicago Mercantile Exchange (CME)
Derivative [Line Items]
Derivative asset, reduction in fair value	(271,000)		(271,000)
Derivative liability, reduction in fair value	(595,000)		(595,000)
Credit-risk-related contingent features
Derivative [Line Items]
Aggregate fair value of derivative instruments in net liability position	11,400,000		11,400,000		6,300,000
Collateral posted	$ 11,300,000		$ 11,300,000		$ 6,200,000
Oil | Commodity swaps and options | Derivatives not designated as hedging instruments | Chicago Mercantile Exchange (CME)
Derivative [Line Items]
Notional amount of commodity contracts in number of barrels of oil and gas | Boe			264
Natural gas | Commodity swaps and options | Derivatives not designated as hedging instruments | Chicago Mercantile Exchange (CME)
Derivative [Line Items]
Notional amount of commodity contracts in number of barrels of oil and gas | MMBTU			5.2