Fair Value of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments not Carried at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 13,612,463	$ 14,115,272
Net loans	37,900,933	32,859,712
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	15,687,776	6,781,783
Held-to-maturity securities	12,982,223	13,842,946
Non-marketable securities not measured at net asset value	228,564	195,405
Non-marketable securities measured at net asset value	293,269	235,351
FHLB and Federal Reserve Bank stock	61,232	60,258
Non-maturity deposits	84,438,332	61,569,714
Time deposits	334,687	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	19,068	17,430
Carrying Amount \| 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	348,257	347,987
Carrying Amount \| 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	495,173
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	15,687,776	6,781,783
Held-to-maturity securities	13,612,463	14,115,272
Non-marketable securities not measured at net asset value	228,564	195,405
Non-marketable securities measured at net asset value	293,269	235,351
FHLB and Federal Reserve Bank stock	61,232	60,258
Non-maturity deposits	84,438,332	61,569,714
Time deposits	273,785	187,980
Commitments to extend credit	34,126	27,197
Estimate of Fair Value Measurement \| Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	19,068	17,430
Estimate of Fair Value Measurement \| 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	378,606	366,856
Estimate of Fair Value Measurement \| 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	557,495
Estimate of Fair Value Measurement \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	15,687,776	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	84,438,332	61,569,714
Time deposits	0	0
Commitments to extend credit	0	0
Estimate of Fair Value Measurement \| Level 1 \| Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimate of Fair Value Measurement \| Level 1 \| 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Estimate of Fair Value Measurement \| Level 1 \| 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0
Estimate of Fair Value Measurement \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Held-to-maturity securities	13,612,463	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	273,785	187,980
Commitments to extend credit	0	0
Estimate of Fair Value Measurement \| Level 2 \| Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	19,068	17,430
Estimate of Fair Value Measurement \| Level 2 \| 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	378,606	366,856
Estimate of Fair Value Measurement \| Level 2 \| 3.125% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	557,495
Estimate of Fair Value Measurement \| 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	228,564	195,405
Non-marketable securities measured at net asset value	0	0
FHLB and Federal Reserve Bank stock	61,232	60,258
Non-maturity deposits	0	0
Time deposits	0	0
Commitments to extend credit	34,126	27,197
Estimate of Fair Value Measurement \| Level 3 \| Short-term borrowings
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term borrowings	0	0
Estimate of Fair Value Measurement \| Level 3 \| 3.50% Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	0	0
Estimate of Fair Value Measurement \| 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	33,552,513	29,104,532
Commercial loans \| Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	34,091,696	29,615,176
Commercial loans \| Estimate of Fair Value Measurement \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans \| Estimate of Fair Value Measurement \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Commercial loans \| Estimate of Fair Value Measurement \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	34,091,696	29,615,176
Consumer loans \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	4,348,420	3,755,180
Consumer loans \| Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	4,418,614	3,820,804
Consumer loans \| Estimate of Fair Value Measurement \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans \| Estimate of Fair Value Measurement \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	0	0
Consumer loans \| Estimate of Fair Value Measurement \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net loans	$ 4,418,614	$ 3,820,804

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Fair Value, Investments, Entities that Calculate Net Asset Value, Non-Marketable Securities

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The amount shown on the books that a bank with insufficient reserves borrows, at the federal funds rate, from another bank to meet its reserve requirements and the amount of securities that an institution sells and agrees to repurchase at a specified date for a specified price, net of any reductions or offsets. Also reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Investment in Federal Home Loan Bank Stock and Federal Reserve Bank, Fair Value Disclosure

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Non-marketable securities accounted for under cost and equity method accounting

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

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