Stockholders' Equity (Narrative) (Details) - USD ($)		3 Months Ended
	Jan. 19, 2022	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2020	Dec. 31, 2021	Oct. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000			10,000,000
Stockholders' equity		$ 11,409,800,000	$ 11,457,900,000		$ 12,016,800,000		$ 11,688,300,000
Common stock dividends (in usd per share)		$ 0.70		$ 0.70
Stock repurchase, shares (in shares)		295,410
Stock repurchase program, number of shares authorized to be repurchased (in shares)						25,000,000
Stock repurchase, aggregate cost		$ 33,800,000	135,600,000
Average price paid per share for common stock repurchased (in usd per share)		$ 114.58
Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 884,900,000	$ 884,900,000		$ 884,900,000		$ 884,900,000
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		5,000			5,000
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 100,000
Depository shares, liquidation preference per share (in dollars per share)		$ 1,000
Preferred stock, annual dividend rate		4.60%
Preferred stock, dividend payment rate, variable rate		3.202%
Common stock dividends (in usd per share)	$ 2,300
Series D Preferred Stock | Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 493,500,000			$ 493,500,000
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000			16,000
Percentage of ownership interest per each depository shares		0.10%
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 25,000
Depository shares, liquidation preference per share (in dollars per share)		$ 25
Preferred stock, annual dividend rate		4.70%
Common stock dividends (in usd per share)	$ 293.75
Series E Preferred Stock | Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 391,400,000			$ 391,400,000
Series D Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		500,000
Preferred stock, shares issued (in shares)		500,000
Percentage of ownership interest per each depository shares		1.00%
Series E Preferred Stock Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000,000
Preferred stock, shares issued (in shares)		16,000,000