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Securities - Additional Information (Details)
$ in Millions
 6 Months Ended
Jun. 30, 2021
USD ($)
Investment
Jun. 30, 2020
USD ($)
Dec. 31, 2020
USD ($)
Investment
Schedule of Investments [Line Items]      
Federal Home Loan Bank stock, at cost | $ $ 686 [1]   $ 714 [2]
Net losses on equity securities | $ $ 0 $ 1  
Collateralized Mortgage Obligations      
Schedule of Investments [Line Items]      
Number of investment securities designated as having a continuous loss position for twelve months or more     4
Capital Trust Notes      
Schedule of Investments [Line Items]      
Number of investment securities designated as having a continuous loss position for twelve months or more 5   5
Asset-backed Securities      
Schedule of Investments [Line Items]      
Number of investment securities designated as having a continuous loss position for twelve months or more 4   7
Corporate Bonds      
Schedule of Investments [Line Items]      
Number of investment securities designated as having a continuous loss position for twelve months or more 5   3
Municipal Bonds      
Schedule of Investments [Line Items]      
Number of investment securities designated as having a continuous loss position for twelve months or more 1   1
[1] Carrying value and estimated fair value are at cost.
[2] Carrying value and estimated fair value are at cost.