Equity (Preferred Stock & Common Stock Repurchase Program - Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	May 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Feb. 06, 2020
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		$ 180	$ 142	$ 136	$ 52
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
Depositary Shares, each representing a 1/1,000th interest in a share of 6.600% Non-Cumulative Preferred Stock, Series A
Class of Stock [Line Items]
Preferred stock, annual dividend rate						6.60%		6.60%
Preferred stock, shares issued		17,000				17,000		17,000
Authorization Under 10b5-1 Plan
Class of Stock [Line Items]
Stock repurchase program, authorized amount									$ 500
Treasury stock, shares acquired						13,250,927	4,993,424
Treasury stock, value acquired						$ 322	$ 188
Stock repurchase program, remaining authorized repurchase amount		$ 231				$ 231