Equity (Preferred Stock & Common Stock Repurchase Program - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		9 Months Ended
	May 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Feb. 06, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Preferred stock, shares issued		33,100				33,100			17,000
Preferred stock, proceeds from issuance, net of issuance costs						$ 390	$ 412
Treasury stock, value acquired		$ 54	$ 126	$ 322	$ 188
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, annual dividend rate	6.75%					6.75%
Preferred stock, shares issued	16,100	16,100				16,100			0
Preferred stock, stated amount per share	$ 25,000
Preferred stock, proceeds from issuance, net of issuance costs	$ 390
Preferred stock, issuance costs	$ 13
Authorization Under 10b5-1 Plan
Class of Stock [Line Items]
Stock repurchase program, authorized amount								$ 500
Treasury stock, shares acquired						15,119,010	8,395,371
Treasury stock, value acquired						$ 376	$ 314
Stock repurchase program, remaining authorized repurchase amount		$ 177				$ 177