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Fair Value (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Fair Value [Line Items]    
Transfers Into Level 3 $ 0 $ 0
Transfers out of Level 3 0 0
Significant fair value adjustments for assets and liabilities measured on a nonrecurring basis $ 0 $ 0