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Investment Securities (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Investments_In_Single_Issuer	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Investment [Line Items]
Percentage decrease requiring a review for impairment	20.00%
Fair value of securities on other-than-temporary impairment watch list	$ 31,000,000.0	$ 51,600,000
Portfolio securities aggregate fair value loss position	948,200,000	1,700,000,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	6,400,000
Available for sale securities in loss position at period end, change in unrealized loss	(6,500,000)
Securities pledged as collateral	4,800,000,000	4,300,000,000
Securities pledged and may be sold or re-pledged	$ 214,200,000
Number of investments in a single issuer that exceed 10% of stockholder's equity | Investments_In_Single_Issuer	0
No investment in a single issuer exceeds this percentage of stockholder's equity	10.00%
Visa Class B Shares [Member]
Investment [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 0
US Treasury and Government [Member]
Investment [Line Items]
U.S. Treasury inflation-protected securities held	434,600,000
Available-for-sale Securities [Member]
Investment [Line Items]
Net gains realized on sales of AFS debt securities	21,096,000	$ 2,354,000	$ 448,000
Private Equity Funds [Member]
Investment [Line Items]
Fair value adjustments, net	$ (10,100,000)

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AFS securities in loss position at period-end, change in unrealized loss.

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The number of investments in a single issuer that exceed 10% of stockholder's equity, excluding obligations of various government-sponsored enterprises such as FNMA, FHLB, and FHLMC.

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