Stockholders' Equity (Narrative) (Details) - USD ($)		3 Months Ended		6 Months Ended
	Apr. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jan. 30, 2019
Class of Stock [Line Items]
Preferred stock, par value (USD per share)				$ 0.01		$ 0.01
Liquidation preference per share (USD per share)	$ 1,000
Proceeds from offering	$ 2,470,000,000
Shares repurchased		$ 1,220,000,000			$ 1,220,000,000
Depositary Shares [Member]
Class of Stock [Line Items]
Ownership interest	1.00%
Series G Preferred Stock [Member]
Class of Stock [Line Items]
Number of shares issued (in shares)	2,500,000
Fixed rate	5.375%			5.375%
Preferred stock, par value (USD per share)	$ 0.01
Liquidation preference per share (USD per share)	$ 100,000			$ 100,000
Common Stock [Member]
Class of Stock [Line Items]
Share repurchase, authorized amount							$ 4,000,000,000.0
Shares repurchased (in shares)		29,000,000	0	0
Shares repurchased		$ 1,200,000,000