Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 14,115,272	$ 15,188,236
Net loans	32,859,712	28,057,377
Time deposits	188,093	50,726
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6,781,783	3,571,539
Held-to-maturity securities	13,842,946	15,487,442
Non-marketable securities not measured at net asset value	195,405	131,453
Non-marketable securities measured at net asset value	235,351	151,247
FHLB and FRB stock	60,258	58,878
Non-maturity deposits	61,569,714	49,278,174
Time deposits	188,093	50,726
Commitments to extend credit	0	0
Carrying Amount | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	17,430	631,412
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	347,987	347,639
Carrying Amount | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes		348,826
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6,781,783	3,571,539
Held-to-maturity securities	14,115,272	15,188,236
Non-marketable securities not measured at net asset value	195,405	131,453
Non-marketable securities measured at net asset value	235,351	151,247
FHLB and FRB stock	60,258	58,878
Non-maturity deposits	61,569,714	49,278,174
Time deposits	187,980	50,337
Commitments to extend credit	27,197	22,930
Estimated Fair Value | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	17,430	631,412
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	366,856	336,088
Estimated Fair Value | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes		361,281
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6,781,783	3,571,539
Held-to-maturity securities	0	0
Non-marketable securities not measured at net asset value	0	0
FHLB and FRB stock	0	0
Non-maturity deposits	61,569,714	49,278,174
Time deposits	0	0
Commitments to extend credit	0	0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes		0
Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	14,115,272	15,188,236
Non-marketable securities not measured at net asset value	0	0
FHLB and FRB stock	0	0
Non-maturity deposits	0	0
Time deposits	187,980	50,337
Commitments to extend credit	0	0
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	17,430	631,412
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes	366,856	336,088
Estimated Fair Value | Significant Other Observable Inputs (Level 2) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes		361,281
Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	0	0
Non-marketable securities not measured at net asset value	195,405	131,453
FHLB and FRB stock	60,258	58,878
Non-maturity deposits	0	0
Time deposits	0	0
Commitments to extend credit	27,197	22,930
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | Other short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Significant Unobservable Inputs (Level 3) | 5.375% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior Notes		0
Commercial loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	29,104,532	25,043,671
Commercial loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	29,615,176	25,463,968
Commercial loans | Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans | Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	29,615,176	25,463,968
Consumer loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,755,180	3,013,706
Consumer loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,820,804	3,064,093
Consumer loans | Estimated Fair Value | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans | Estimated Fair Value | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans | Estimated Fair Value | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	$ 3,820,804	$ 3,064,093