Investments (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Equity Securities, FV-NI	$ 9,200,000	$ 11,800,000
Federal Home Loan Bank Stock and Federal Reserve Bank Stock	15,300,000	15,500,000
Certificates of Deposit, at Carrying Value	1,000,000	2,000,000
nongovernmentalissuerover10%ofequity	0	0
Credit-related net investment impairment losses	0	0	$ 0
Asset Pledged as Collateral
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 711,000,000	$ 644,000,000
VISA, Inc. (VISA)
Schedule of Investments [Line Items]
Investment Owned, Balance, Shares		86,605
Debt and Equity Securities, Realized Gain (Loss)		$ 17,800,000
Investment Owned, Balance, Principal Amount		$ 0

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Amount of restricted 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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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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Amount of Federal Home Loan Bank (FHLB) and Federal Reserve Bank stock.

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For investments which are quantified by principal amount, the principle balance held at close of period.

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Balance held at close of period in number of shares.

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