Investment Securities - Summary of Remaining Contractual Principal Maturities for Available-for-Sale Securities (Details) $ in Thousands	3 Months Ended
Sep. 30, 2020 USD ($)
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	$ 25,904,324
One Year or Less	83,670
After One Year to Five Years	2,989,181
After Five Years to Ten Years	3,081,965
After Ten Years	$ 19,749,508
Available-for-sale Securities \| Lower Limit
Debt Securities, Available-for-sale [Line Items]
Mortgage-backed securities contractual maturities (in years)	10 years
Available-for-sale Securities \| Upper Limit
Debt Securities, Available-for-sale [Line Items]
Mortgage-backed securities contractual maturities (in years)	30 years
Available-for-sale Securities \| U.S. treasury securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	$ 4,547,294
One Year or Less	60,221
After One Year to Five Years	2,989,181
After Five Years to Ten Years	1,497,892
After Ten Years	0
Available-for-sale Securities \| U.S. agency debentures
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	152,526
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	152,526
After Ten Years	0
Available-for-sale Securities \| Foreign government debt securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	23,449
One Year or Less	23,449
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	0
Available-for-sale Securities \| Residential mortgage-backed securities \| Agency-issued mortgage-backed securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	9,770,313
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	9,770,313
Available-for-sale Securities \| Residential mortgage-backed securities \| Agency-issued collateralized mortgage obligations—fixed rate
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	7,315,973
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	0
After Ten Years	7,315,973
Available-for-sale Securities \| Agency-issued commercial mortgage-backed securities
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Total	4,094,769
One Year or Less	0
After One Year to Five Years	0
After Five Years to Ten Years	1,431,547
After Ten Years	$ 2,663,222

The period (in years) that is typical for contractual maturities of mortgage-backed securities.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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