Derivatives (Narrative) (Details) MMBTU in Thousands, Boe in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020 USD ($) Boe MMBTU company	Dec. 31, 2019 USD ($) MMBTU Boe company
Derivative [Line Items]
Derivative liabilities - Fair value	$ 506,019	$ 256,528
Derivative assets - Fair value	708,610	330,316
Credit-risk-related contingent features
Derivative [Line Items]
Aggregate fair value of derivative instruments in net liability position	126,400	56,400
Derivative asset		14,400
Derivative liability		70,800
Collateral posted	126,300	56,400
Derivative instruments designated as hedging instruments
Derivative [Line Items]
Notional amount	371,186	117,193
Derivative liabilities - Fair value	2,113	4,784
Derivative assets - Fair value	64	0
Derivative instruments designated as hedging instruments \| Interest rate contracts \| Cash Flow Hedging
Derivative [Line Items]
Notional amount	275,000	0
Net unrealized gains, net of tax, recorded in AOCI expected to be reclassified into earnings during next 12 months	536
Derivative liabilities - Fair value	1,861	0
Derivative assets - Fair value	0	0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	19,523,762	20,540,031
Derivative liabilities - Fair value	503,906	251,744
Derivative assets - Fair value	708,546	330,316
Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	1,832,383	4,839,661
Derivative liabilities - Fair value	14,530	47,024
Derivative assets - Fair value	19,134	54,637
Derivatives not designated as hedging instruments \| Interest rate contracts
Derivative [Line Items]
Notional amount	17,613,982	15,489,692
Derivative liabilities - Fair value	370,196	124,119
Derivative assets - Fair value	566,571	192,883
Derivatives not designated as hedging instruments \| Interest rate contracts \| Financial Counterparty
Derivative [Line Items]
Notional amount	8,820,000	7,750,000
Derivatives not designated as hedging instruments \| Interest rate contracts \| LCH
Derivative [Line Items]
Notional amount	2,990,000	2,530,000
Derivative liabilities - Fair value	215,900	75,100
Derivative assets - Fair value		2,900
Derivatives not designated as hedging instruments \| Credit contracts
Derivative [Line Items]
Notional amount	77,397	210,678
Derivative liabilities - Fair value	307	84
Derivative assets - Fair value	$ 47	$ 2
Weighted average remaining maturity of outstanding RPAs	4 years	2 years 2 months 12 days
Derivatives not designated as hedging instruments \| Credit contracts \| RPA protection sold
Derivative [Line Items]
Maximum exposure of RPAs with protection sold	$ 748	$ 125
Derivatives not designated as hedging instruments \| Equity, Public Companies
Derivative [Line Items]
Number of companies that issued the equity (issuers portion only) \| company	3	3
Derivatives not designated as hedging instruments \| Equity contracts
Derivative [Line Items]
Notional amount	$ 0	$ 0
Derivative liabilities - Fair value	0	0
Derivative assets - Fair value	12,765	1,414
Derivatives not designated as hedging instruments \| Commodity contracts
Derivative [Line Items]
Notional amount	0	0
Derivative liabilities - Fair value	118,873	80,517
Derivative assets - Fair value	110,029	81,380
Derivatives not designated as hedging instruments \| Commodity contracts \| Chicago Mercantile Exchange (CME)
Derivative [Line Items]
Derivative liabilities - Fair value	6,600	1,500
Derivative assets - Fair value	17,800	2,900
Derivative assets (liabilities), at fair value, net	$ 0	$ 986
Derivatives not designated as hedging instruments \| Commodity contracts \| Chicago Mercantile Exchange (CME) \| Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure \| Boe	1,506	1,752
Derivatives not designated as hedging instruments \| Commodity contracts \| Chicago Mercantile Exchange (CME) \| Natural gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, energy measure \| MMBTU	31,395	6,075
Derivatives not designated as hedging instruments \| Equity, Private Companies
Derivative [Line Items]
Number of companies that issued the equity (issuers portion only) \| company	17	18
Maximum \| Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Original maturity (in years)	1 year	1 year
Derivative Financial Instruments, Liabilities \| Derivative instruments designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	$ 81,000	$ 86,200
Derivative liabilities - Fair value	$ 252	$ 1,600

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