Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 13,541,461	$ 14,115,272
Net loans	36,137,394	32,859,712
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	14,202,106	6,781,783
Held-to-maturity securities	12,858,823	13,842,946
Non-marketable securities not measured at net asset value	226,236	195,405
Non-marketable securities measured at net asset value	252,513	235,351
FHLB and Federal Reserve Bank stock	60,673	60,258
Non-maturity deposits	74,128,263	61,569,714
Time deposits	377,501	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	50,924	17,430
Carrying Amount | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	348,166	347,987
Carrying Amount | 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	495,054
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	14,202,106	6,781,783
Held-to-maturity securities	13,541,461	14,115,272
Non-marketable securities not measured at net asset value	226,236	195,405
Non-marketable securities measured at net asset value	252,513	235,351
FHLB and Federal Reserve Bank stock	60,673	60,258
Non-maturity deposits	74,128,263	61,569,714
Time deposits	376,762	187,980
Commitments to extend credit	31,432	27,197
Estimated Fair Value | Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	50,924	17,430
Estimated Fair Value | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	380,314	366,856
Estimated Fair Value | 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	537,115
Estimated Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	14,202,106	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	74,128,263	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 1 | 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	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	13,541,461	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	376,762	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	50,924	17,430
Estimated Fair Value | Level 2 | 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	380,314	366,856
Estimated Fair Value | Level 2 | 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	537,115
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	226,236	195,405
Non-marketable securities measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	60,673	60,258
Non-maturity deposits	0	0
Time deposits	0	0
Commitments to extend credit	31,432	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
Estimated Fair Value | Level 3 | 3.125% 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	32,412,462	29,104,532
Commercial loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	32,728,159	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	32,728,159	29,615,176
Consumer loans | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,724,932	3,755,180
Consumer loans | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	3,761,539	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	$ 3,761,539	$ 3,820,804