Debt and Credit Arrangements (Schedule of Debt) (Parenthetical) (Details)		12 Months Ended
	Sep. 19, 2020	Dec. 31, 2020	Dec. 31, 2019
Senior debentures maturing April 15, 2026 [Member]
Debt Instrument [Line Items]
Maturity date		Apr. 15, 2026	Apr. 15, 2026
Senior debentures maturing September 1, 2030 [Member]
Debt Instrument [Line Items]
Maturity date		Sep. 01, 2030	Sep. 01, 2030
Senior debentures maturing October 15, 2025 [Member]
Debt Instrument [Line Items]
Maturity date		Oct. 15, 2025	Oct. 15, 2025
Subordinated debentures maturing February 3, 2027 [Member]
Debt Instrument [Line Items]
Maturity date		Feb. 03, 2027	Feb. 03, 2027
Subordinated debentures maturing March 30, 2053 [Member]
Debt Instrument [Line Items]
Maturity date	Mar. 30, 2053	Mar. 30, 2053	Mar. 30, 2053