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Derivatives (Narrative) (Details) MMBTU in Thousands, Boe in Thousands, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 USD ($) Boe MMBTU company | Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($) Boe MMBTU company
Derivative [Line Items] |  |  |
Derivative assets - Fair value | $ 457,317 |  | $ 602,754
Derivative liabilities - Fair value | 344,135 |  | 424,828
Credit-risk-related contingent features |  |  |
Derivative [Line Items] |  |  |
Aggregate fair value of derivative instruments in net liability position | 64,900 |  | 107,400
Collateral posted | 64,900 |  | 106,800
Derivative instruments designated as hedging instruments |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 908 |  | 0
Notional Amount | 358,936 |  | 359,269
Derivative liabilities - Fair value | 1,258 |  | 2,099
Derivative instruments designated as hedging instruments | Fair Value Hedging | Interest Expense |  |  |
Derivative [Line Items] |  |  |
Gains or losses recognized on Consolidated Statement of Income related to the derivatives designated as fair value hedges |  | $ (1,400) |
Derivative instruments designated as hedging instruments | Fair Value Hedging | Interest Expense | Deposits |  |  |
Derivative [Line Items] |  |  |
Gains or losses recognized on Consolidated Statement of Income related to the derivatives designated as fair value hedges | 0 |  |
Derivative instruments designated as hedging instruments | Interest rate contracts | Cash Flow Hedging |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 0 |  | 0
Net unrealized losses, net of tax, recorded in AOCI expected to be reclassified into earnings during next 12 months | (560) |  |
Notional Amount | 275,000 |  | 275,000
Derivative liabilities - Fair value | 1,258 |  | 1,864
Derivative instruments designated as hedging instruments | Interest rate contracts | Fair Value Hedging |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 0 |  | 0
Derivative instruments designated as hedging instruments | Interest rate contracts | Fair Value Hedging | Interest Expense |  |  |
Derivative [Line Items] |  |  |
Change in unrealized gains or losses on fair value hedging instruments | 0 | $ 2,000 |
Derivatives not designated as hedging instruments |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 456,409 |  | 602,754
Notional Amount | 22,005,910 |  | 21,341,158
Derivative liabilities - Fair value | 342,877 |  | 422,729
Derivatives not designated as hedging instruments | Foreign exchange contracts |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 38,654 |  | 30,300
Notional Amount | 4,036,958 |  | 3,108,488
Derivative liabilities - Fair value | 27,287 |  | 22,524
Derivatives not designated as hedging instruments | Interest rate contracts |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 319,049 |  | 489,132
Notional Amount | 17,891,960 |  | 18,155,678
Derivative liabilities - Fair value | 229,032 |  | 315,834
Derivatives not designated as hedging instruments | Interest rate contracts | Financial Counterparty |  |  |
Derivative [Line Items] |  |  |
Notional Amount | 8,960,000 |  | 9,090,000
Derivatives not designated as hedging instruments | Interest rate contracts | LCH |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 27,200 |  | 1,300
Notional Amount | 2,930,000 |  | 2,980,000
Derivative liabilities - Fair value | 116,200 |  | 187,400
Derivatives not designated as hedging instruments | Credit contracts |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 5 |  | 13
Notional Amount | 76,992 |  | 76,992
Derivative liabilities - Fair value | 153 |  | 206
Derivatives not designated as hedging instruments | Credit contracts | RPAs - protection sold |  |  |
Derivative [Line Items] |  |  |
Maximum exposure of RPAs with protection sold | $ 4,900 |  | $ 6,000
Weighted average remaining maturity of outstanding RPAs | 3 years 3 months 18 days |  | 3 years 6 months
Derivatives not designated as hedging instruments | Equity, Public Companies |  |  |
Derivative [Line Items] |  |  |
Number of companies that issued the equity (issuers portion only) | company |  |  | 2
Derivatives not designated as hedging instruments | Equity contracts |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | $ 272 |  | $ 858
Notional Amount | 0 |  | 0
Derivative liabilities - Fair value | 0 |  | 0
Derivatives not designated as hedging instruments | Commodity contracts |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 98,429 |  | 82,451
Notional Amount | 0 |  | 0
Derivative liabilities - Fair value | 86,405 |  | 84,165
Derivatives not designated as hedging instruments | Commodity contracts | Chicago Mercantile Exchange (CME) |  |  |
Derivative [Line Items] |  |  |
Derivative assets - Fair value | 897 |  | 7,900
Derivative liabilities - Fair value | 10,000 |  | 3,700
Derivative assets (liabilities), at fair value, net | $ 0 |  | $ 0
Derivatives not designated as hedging instruments | Commodity contracts | Chicago Mercantile Exchange (CME) | Oil |  |  |
Derivative [Line Items] |  |  |
Derivative, nonmonetary notional amount, energy measure | Boe | 1,320 |  | 1,275
Derivatives not designated as hedging instruments | Commodity contracts | Chicago Mercantile Exchange (CME) | Natural gas |  |  |
Derivative [Line Items] |  |  |
Derivative, nonmonetary notional amount, energy measure | MMBTU | 27,850 |  | 29,733
Derivatives not designated as hedging instruments | Equity, Private Companies |  |  |
Derivative [Line Items] |  |  |
Number of companies that issued the equity (issuers portion only) | company | 18 |  | 17
Maximum | Derivatives not designated as hedging instruments | Foreign exchange contracts |  |  |
Derivative [Line Items] |  |  |
Original maturity (in years) | 1 year |  | 1 year

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