Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 14,131,154	$ 14,115,272
Net loans	35,419,122	32,859,712
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	9,561,448	6,781,783
Held-to-maturity securities	13,574,289	13,842,946
Non-marketable securities not measured at net asset value	190,959	195,405
Non-marketable securities measured at net asset value	224,669	235,351
FHLB and Federal Reserve Bank stock	116,323	60,258
Non-maturity deposits	61,738,032	61,569,714
Time deposits	173,925	188,093
Commitments to extend credit	0	0
Carrying Amount | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	3,138,162	17,430
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	348,076	347,987
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	9,561,448	6,781,783
Held-to-maturity securities	14,131,154	14,115,272
Non-marketable securities not measured at net asset value	190,959	195,405
Non-marketable securities measured at net asset value	224,669	235,351
FHLB and Federal Reserve Bank stock	116,323	60,258
Non-maturity deposits	61,738,032	61,569,714
Time deposits	173,855	187,980
Commitments to extend credit	27,162	27,197
Estimated Fair Value | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	3,138,162	17,430
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	363,878	366,856
Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	9,561,448	6,781,783
Held-to-maturity securities	0	0
Non-marketable securities not measured at net asset value	0	0
Non-marketable securities measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Non-maturity deposits	61,738,032	61,569,714
Time deposits	0	0
Commitments to extend credit	0	0
Estimated Fair Value | Level 1 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Level 1 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	14,131,154	14,115,272
Non-marketable securities not measured at net asset value	0	0
Non-marketable securities measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	0	0
Non-maturity deposits	0	0
Time deposits	173,855	187,980
Commitments to extend credit	0	0
Estimated Fair Value | Level 2 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	3,138,162	17,430
Estimated Fair Value | Level 2 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	363,878	366,856
Estimated Fair Value | 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	190,959	195,405
Non-marketable securities measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	116,323	60,258
Non-maturity deposits	0	0
Time deposits	0	0
Commitments to extend credit	27,162	27,197
Estimated Fair Value | Level 3 | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimated Fair Value | Level 3 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Commercial loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	31,837,622	29,104,532
Commercial loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	32,128,958	29,615,176
Commercial loans | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	32,128,958	29,615,176
Consumer loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,581,500	3,755,180
Consumer loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,614,597	3,820,804
Consumer loans | Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans | Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	$ 3,614,597	$ 3,820,804