Investment securities available for sale transferred to held to maturity amortized cost at date of transfer.

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Investment securities available for sale transferred to held to maturity fair value at date of transfer.

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Other Comprehensive Income Loss Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity Arising During Period Before Tax

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Unrealized Losses Related to Marketability of Securities or Issuer's Ability to Honor Redemption Obligations

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities.

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Balance held at close of period in number of shares.

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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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Investments (Narrative) (Details) shares in Thousands	3 Months Ended		9 Months Ended
Investments (Narrative) (Details) shares in Thousands	Sep. 30, 2018 USD ($) investment investments shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) investment investments shares	Sep. 30, 2017 USD ($)	May 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Schedule of Investments [Line Items]
Investment in marketable equity securities	$ 109,907,000		$ 109,907,000			$ 0
Investment securities available for sale	4,677,351,000		4,677,351,000			7,180,180,000
Unrealized losses on available for sale securities transferred to held to maturity included in comprehensive income	$ 0	$ 0	$ (109,507,000)	$ 0
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions \| investment	185		185
Held-to-maturity, securities in unrealized loss positions, qualitative disclosure, number of positions \| investment	2		2
Unrealized losses related to marketability of securities or issuer's ability to honor redemption obligations	$ 0		$ 0
Investment value deemed to be OTTI	0
Investment securities, aggregate carrying value, pledged as collateral	3,530,000,000		3,530,000,000			4,590,000,000
Equity Securities
Schedule of Investments [Line Items]
Investment securities available for sale	0		0			105,208,000
Mortgage Backed Securities
Schedule of Investments [Line Items]
Investment securities available for sale	$ 2,919,796,000		$ 2,919,796,000			5,340,756,000
Investment securities available for sale transferred to held to maturity amortized cost					$ 2,490,000,000
Investment securities available for sale transferred to held to maturity fair value					$ 2,380,000,000
Available-for-sale, securities in unrealized loss positions, number of positions, greater than or equal to one year \| investments	183		183
U. S. Treasury
Schedule of Investments [Line Items]
Investment securities available for sale	$ 1,505,434,000		$ 1,505,434,000			1,657,864,000
Corporate Bonds
Schedule of Investments [Line Items]
Investment securities available for sale	$ 119,933,000		$ 119,933,000			$ 59,963,000
Available-for-sale, securities in unrealized loss positions, number of positions, greater than or equal to one year \| investments	1		1
Financial Instruments ASU cumulative effect adjustment
Schedule of Investments [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ 18,700,000		$ 18,700,000
Visa Class B Common Stock
Schedule of Investments [Line Items]
Investment owned (in shares) \| shares	298		298
Investment owned, fair value	$ 0		$ 0
U. S. Treasury
Schedule of Investments [Line Items]
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, number of positions \| investment	1		1