Derivatives (Notional and Fair Values) (Details) MMBTU in Thousands, Boe in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019 USD ($) Boe MMBTU company	Dec. 31, 2018 USD ($) Boe MMBTU company
Derivative Asset [Abstract]
Derivative assets - Fair value	$ 358,639	$ 107,816
Less: Master netting agreements	(62,741)	(31,569)
Less: Cash collateral received/paid	(6,587)	(13,577)
Derivative asset, after netting	289,311	62,670
Derivative Liability [Abstract]
Derivative liabilities - Fair value	263,734	118,305
Less: Master netting agreements	(62,741)	(31,569)
Less: Cash collateral received/paid	(47,979)	(6,833)
Derivative liability, after netting	$ 153,014	$ 79,903
Crude oil \| Customer Counterparty
Derivative Liability [Abstract]
Derivative, nonmonetary notional amount, energy measure \| Boe	7,166	2,507
Natural gas \| Customer Counterparty
Derivative Liability [Abstract]
Derivative, nonmonetary notional amount, energy measure \| MMBTU	33,089	14,722
Derivative instruments designated as hedging instruments
Derivative Instruments
Notional amount	$ 115,857	$ 126,056
Derivative Asset [Abstract]
Derivative assets - Fair value	0	0
Derivative Liability [Abstract]
Derivative liabilities - Fair value	3,235	6,477
Derivative instruments designated as hedging instruments \| Interest rate contracts
Derivative Instruments
Notional amount	31,026	35,811
Derivative Asset [Abstract]
Derivative assets - Fair value	0	0
Derivative Liability [Abstract]
Derivative liabilities - Fair value	2,804	5,866
Derivative instruments designated as hedging instruments \| Foreign exchange contracts
Derivative Instruments
Notional amount	84,831	90,245
Derivative Asset [Abstract]
Derivative assets - Fair value	0	0
Derivative Liability [Abstract]
Derivative liabilities - Fair value	431	611
Derivatives not designated as hedging instruments
Derivative Instruments
Notional amount	18,988,712	15,222,341
Derivative Asset [Abstract]
Derivative assets - Fair value	358,639	107,816
Derivative Liability [Abstract]
Derivative liabilities - Fair value	260,499	111,828
Derivatives not designated as hedging instruments \| Interest rate contracts
Derivative Instruments
Notional amount	14,139,233	11,695,499
Derivative Asset [Abstract]
Derivative assets - Fair value	264,603	69,818
Derivative Liability [Abstract]
Derivative liabilities - Fair value	168,113	69,267
Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative Instruments
Notional amount	4,638,136	3,407,522
Derivative Asset [Abstract]
Derivative assets - Fair value	59,512	21,624
Derivative Liability [Abstract]
Derivative liabilities - Fair value	50,397	19,329
Derivatives not designated as hedging instruments \| Credit contracts
Derivative Instruments
Notional amount	211,343	119,320
Derivative Asset [Abstract]
Derivative assets - Fair value	4	1
Derivative Liability [Abstract]
Derivative liabilities - Fair value	122	164
Derivatives not designated as hedging instruments \| Equity contracts
Derivative Instruments
Notional amount	0	0
Derivative Asset [Abstract]
Derivative assets - Fair value	1,542	1,951
Derivative Liability [Abstract]
Derivative liabilities - Fair value	0	0
Derivatives not designated as hedging instruments \| Commodity contracts
Derivative Instruments
Notional amount	0	0
Derivative Asset [Abstract]
Derivative assets - Fair value	32,978	14,422
Derivative Liability [Abstract]
Derivative liabilities - Fair value	$ 41,867	$ 23,068
Derivatives not designated as hedging instruments \| Equity, Public Companies
Derivative Liability [Abstract]
Number of companies that issued the equity (issuers portion only) \| company	3	4
Derivatives not designated as hedging instruments \| Equity, Private Companies
Derivative Liability [Abstract]
Number of companies that issued the equity (issuers portion only) \| company	17	18
Commodity contracts \| Derivatives not designated as hedging instruments \| Commodity contracts \| Customer Counterparty
Derivative Asset [Abstract]
Derivative assets - Fair value	$ 4,289	$ 1,127
Derivative Liability [Abstract]
Derivative liabilities - Fair value	36,147	22,687
Commodity contracts \| Derivatives not designated as hedging instruments \| Commodity contracts \| Crude oil \| Customer Counterparty
Derivative Asset [Abstract]
Derivative assets - Fair value	1,473	0
Derivative Liability [Abstract]
Derivative liabilities - Fair value	$ 28,634	$ 20,678
Derivative, nonmonetary notional amount, energy measure \| Boe	7,166	2,507
Commodity contracts \| Derivatives not designated as hedging instruments \| Commodity contracts \| Natural gas \| Customer Counterparty
Derivative Asset [Abstract]
Derivative assets - Fair value	$ 2,816	$ 1,127
Derivative Liability [Abstract]
Derivative liabilities - Fair value	$ 7,513	$ 2,009
Derivative, nonmonetary notional amount, energy measure \| MMBTU	33,089	14,722

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