Equity (Preferred Stock - Authorized, Issued and Outstanding) (Details) - $ / shares	Dec. 31, 2020	Sep. 01, 2020	Dec. 31, 2019
Preferred stock authorized (shares)	20,000,000		20,000,000
Preferred stock outstanding (shares)	36,000		41,000
Common stock held in treasury at cost (shares)	119,000,000		109,000,000
Series B Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 40
Preferred stock outstanding (shares)	1,000		1,000
Series O Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 100,000
Preferred stock outstanding (shares)	10,000		10,000
Series P Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 100,000
Preferred stock outstanding (shares)	15,000		15,000
Series Q Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 100,000
Preferred stock outstanding (shares)			5,000
Treasury stock, preferred (shares)		4,800
Series R Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 100,000
Preferred stock outstanding (shares)	5,000		5,000
Series S Preferred Stock
Preferred stock, liquidation preference per share (in USD per share)	$ 100,000
Preferred stock outstanding (shares)	5,000		5,000
Depositary Shares
Common stock held in treasury at cost (shares)		19,200,000