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Fair Value Measurements (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Supplemental Executive Retirement Plans [Member]      
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Change in unrealized gains (losses) included in other income $ 5,000,000.0 $ (700,000) $ 4,500,000