Stockholders' Equity (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock
Shares reserved for issuance under stock plans, dividend reinvestment program and conversion of Preferred and Preference Stock	41,956,401
Common Stock
Stock
Shares outstanding (shares)	170,448,943	187,675,082	186,603,738
Repurchases of common stock (shares)		(18,595,315)
Issuance of common stock (shares)	1,526,245	1,276,797	1,043,809
Conversions to common stock (shares)		92,379	27,535
Shares outstanding (shares)	171,975,188	170,448,943	187,675,082
Treasury Stock
Stock
Shares outstanding (shares)	152,888,969	135,662,830	136,734,174
Repurchases of common stock (shares)		18,595,315
Issuance of common stock (shares)	1,526,245	1,276,797	1,043,809
Conversions to common stock (shares)		92,379	27,535
Shares outstanding (shares)	151,362,724	152,888,969	135,662,830