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Derivatives, Fair Value of Derivatives Contracts (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
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Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derviative contracts, net of cash collateral, Assets, Fair value | $ 349,481 |  | $ 220,502 |  | $ 352,559 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 252,387 |  | 171,963 |  | 336,327 |
Not Designated as Hedging Instrument [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 16,964,723 | [1] | 20,038,522 | [2] | 28,952,817 | [3]
Derivative Liabilities, Notional | 19,689,316 | [1] | 20,186,467 | [2] | 26,144,409 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 470,003 |  | 301,052 |  | 402,422 |
Derivative Assets, Netting Adjustments | (103,535) |  | (74,022) |  | (45,885) |
Derivative Assets, Net Fair Value Before Cash Collateral | 366,468 |  | 227,030 |  | 356,537 |
Derivative Assets, Cash Collateral | (16,987) |  | (6,528) |  | (3,978) |
Derviative contracts, net of cash collateral, Assets, Fair value | 349,481 |  | 220,502 |  | 352,559 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 475,005 |  | 302,405 |  | 400,580 |
Derivative Liabilities, Netting Adjustments | (103,535) |  | (74,022) |  | (45,885) |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 371,470 |  | 228,383 |  | 354,695 |
Derivative Liabilities, Cash Collateral | (119,083) |  | (56,420) |  | (18,368) |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 252,387 |  | 171,963 |  | 336,327 |
Not Designated as Hedging Instrument [Member] | Total customer risk management programs |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 15,900,610 | [1] | 15,301,821 | [2] | 17,011,557 | [3]
Derivative Liabilities, Notional | 15,610,222 | [1] | 14,458,046 | [2] | 16,963,878 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 446,116 |  | 291,558 |  | 367,788 |
Derivative Assets, Netting Adjustments | (87,445) |  | (66,929) |  | (45,885) |
Derivative Assets, Net Fair Value Before Cash Collateral | 358,671 |  | 224,629 |  | 321,903 |
Derivative Assets, Cash Collateral | (16,987) |  | (6,528) |  | (3,978) |
Derviative contracts, net of cash collateral, Assets, Fair value | 341,684 |  | 218,101 |  | 317,925 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 438,485 |  | 280,643 |  | 357,390 |
Derivative Liabilities, Netting Adjustments | (87,445) |  | (66,929) |  | (45,885) |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 351,040 |  | 213,714 |  | 311,505 |
Derivative Liabilities, Cash Collateral | (119,083) |  | (56,420) |  | (18,368) |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 231,957 |  | 157,294 |  | 293,137 |
Not Designated as Hedging Instrument [Member] | To-be-announced residential mortgage-backed securities [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 12,423,155 | [1] | 12,347,542 | [2] | 14,244,442 | [3]
Derivative Liabilities, Notional | 12,160,590 | [1] | 11,537,742 | [2] | 14,244,442 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 45,983 |  | 23,606 |  | 38,875 |
Derivative Assets, Netting Adjustments | (18,338) |  | (18,096) |  | (9,547) |
Derivative Assets, Net Fair Value Before Cash Collateral | 27,645 |  | 5,510 |  | 29,328 |
Derivative Assets, Cash Collateral | 0 |  | 0 |  | 0 |
Derviative contracts, net of cash collateral, Assets, Fair value | 27,645 |  | 5,510 |  | 29,328 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 43,074 |  | 20,367 |  | 34,948 |
Derivative Liabilities, Netting Adjustments | (18,338) |  | (18,096) |  | (9,547) |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 24,736 |  | 2,271 |  | 25,401 |
Derivative Liabilities, Cash Collateral | 0 |  | (704) |  | (374) |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 24,736 |  | 1,567 |  | 25,027 |
Not Designated as Hedging Instrument [Member] | Interest rate swaps [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 1,702,731 | [1] | 1,478,944 | [2] | 1,368,210 | [3]
Derivative Liabilities, Notional | 1,702,731 | [1] | 1,478,944 | [2] | 1,368,230 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 46,160 |  | 28,278 |  | 27,016 |
Derivative Assets, Netting Adjustments | (1,300) |  | 0 |  | 0 |
Derivative Assets, Net Fair Value Before Cash Collateral | 44,860 |  | 28,278 |  | 27,016 |
Derivative Assets, Cash Collateral | (13,307) |  | (4,964) |  | (2,820) |
Derviative contracts, net of cash collateral, Assets, Fair value | 31,553 |  | 23,314 |  | 24,196 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 46,162 |  | 28,298 |  | 27,056 |
Derivative Liabilities, Netting Adjustments | (1,300) |  | 0 |  | 0 |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 44,862 |  | 28,298 |  | 27,056 |
Derivative Liabilities, Cash Collateral | (3,844) |  | (12,896) |  | (16,599) |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 41,018 |  | 15,402 |  | 10,457 |
Not Designated as Hedging Instrument [Member] | Energy contracts [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 1,509,976 | [1] | 1,190,067 | [2] | 983,794 | [3]
Derivative Liabilities, Notional | 1,485,036 | [1] | 1,166,924 | [2] | 939,350 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 202,086 |  | 103,044 |  | 45,368 |
Derivative Assets, Netting Adjustments | (67,611) |  | (47,873) |  | (35,166) |
Derivative Assets, Net Fair Value Before Cash Collateral | 134,475 |  | 55,171 |  | 10,202 |
Derivative Assets, Cash Collateral | (3,020) |  | (196) |  | (238) |
Derviative contracts, net of cash collateral, Assets, Fair value | 131,455 |  | 54,975 |  | 9,964 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 200,290 |  | 101,603 |  | 42,744 |
Derivative Liabilities, Netting Adjustments | (67,611) |  | (47,873) |  | (35,166) |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 132,679 |  | 53,730 |  | 7,578 |
Derivative Liabilities, Cash Collateral | (115,191) |  | (42,767) |  | 0 |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 17,488 |  | 10,963 |  | 7,578 |
Not Designated as Hedging Instrument [Member] | Agricultural contracts [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 26,318 | [1] | 53,238 | [2] | 60,745 | [3]
Derivative Liabilities, Notional | 26,316 | [1] | 48,552 | [2] | 60,746 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 1,024 |  | 1,576 |  | 1,870 |
Derivative Assets, Netting Adjustments | (196) |  | (960) |  | (1,172) |
Derivative Assets, Net Fair Value Before Cash Collateral | 828 |  | 616 |  | 698 |
Derivative Assets, Cash Collateral | 0 |  | 0 |  | 0 |
Derviative contracts, net of cash collateral, Assets, Fair value | 828 |  | 616 |  | 698 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 998 |  | 1,551 |  | 1,846 |
Derivative Liabilities, Netting Adjustments | (196) |  | (960) |  | (1,172) |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 802 |  | 591 |  | 674 |
Derivative Liabilities, Cash Collateral | 0 |  | 0 |  | 0 |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 802 |  | 591 |  | 674 |
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 148,824 | [1] | 132,397 | [2] | 252,525 | [3]
Derivative Liabilities, Notional | 145,943 | [1] | 126,251 | [2] | 249,269 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 146,719 |  | 129,551 |  | 249,788 |
Derivative Assets, Netting Adjustments | 0 |  | 0 |  | 0 |
Derivative Assets, Net Fair Value Before Cash Collateral | 146,719 |  | 129,551 |  | 249,788 |
Derivative Assets, Cash Collateral | 0 |  | (448) |  | 0 |
Derviative contracts, net of cash collateral, Assets, Fair value | 146,719 |  | 129,103 |  | 249,788 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 143,817 |  | 123,321 |  | 245,925 |
Derivative Liabilities, Netting Adjustments | 0 |  | 0 |  | 0 |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 143,817 |  | 123,321 |  | 245,925 |
Derivative Liabilities, Cash Collateral | (48) |  | (53) |  | (1,395) |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 143,769 |  | 123,268 |  | 244,530 |
Not Designated as Hedging Instrument [Member] | Equity option contracts [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 89,606 | [1] | 99,633 | [2] | 101,841 | [3]
Derivative Liabilities, Notional | 89,606 | [1] | 99,633 | [2] | 101,841 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 4,144 |  | 5,503 |  | 4,871 |
Derivative Assets, Netting Adjustments | 0 |  | 0 |  | 0 |
Derivative Assets, Net Fair Value Before Cash Collateral | 4,144 |  | 5,503 |  | 4,871 |
Derivative Assets, Cash Collateral | (660) |  | (920) |  | (920) |
Derviative contracts, net of cash collateral, Assets, Fair value | 3,484 |  | 4,583 |  | 3,951 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 4,144 |  | 5,503 |  | 4,871 |
Derivative Liabilities, Netting Adjustments | 0 |  | 0 |  | 0 |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 4,144 |  | 5,503 |  | 4,871 |
Derivative Liabilities, Cash Collateral | 0 |  | 0 |  | 0 |
Derivative Liabilities, Fair Value, Net of Cash Collateral | 4,144 |  | 5,503 |  | 4,871 |
Not Designated as Hedging Instrument [Member] | Internal risk management programs [Member] |  |  |  |  |  |
Notional Amount of Derivatives [Abstract] |  |  |  |  |  |
Derivative Assets, Notional | 1,064,113 | [1] | 4,736,701 | [2] | 11,941,260 | [3]
Derivative Liabilities, Notional | 4,079,094 | [1] | 5,728,421 | [2] | 9,180,531 | [3]
Derivative Assets, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Assets, Gross Fair Value | 23,887 |  | 9,494 |  | 34,634 |
Derivative Assets, Netting Adjustments | (16,090) |  | (7,093) |  | 0 |
Derivative Assets, Net Fair Value Before Cash Collateral | 7,797 |  | 2,401 |  | 34,634 |
Derivative Assets, Cash Collateral | 0 |  | 0 |  | 0 |
Derviative contracts, net of cash collateral, Assets, Fair value | 7,797 |  | 2,401 |  | 34,634 |
Derivative Liabilities, Fair Value, Net [Abstract] |  |  |  |  |  |
Derivative Liabilities, Gross Fair Value | 36,520 |  | 21,762 |  | 43,190 |
Derivative Liabilities, Netting Adjustments | (16,090) |  | (7,093) |  | 0 |
Derivative Liabilities, Net Fair Value Before Cash Collateral | 20,430 |  | 14,669 |  | 43,190 |
Derivative Liabilities, Cash Collateral | 0 |  | 0 |  | 0 |
Derivative Liabilities, Fair Value, Net of Cash Collateral | $ 20,430 |  | $ 14,669 |  | $ 43,190 |
[1] | Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.
[2] | Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.
[3] | Notional amounts for commodity contracts are converted into dollar-equivalent amounts based on dollar prices at the inception of the contract.

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