Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 14, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accelerated Share Repurchases [Line Items]
Treasury stock, common, amount		$ 211	$ 309	$ 250	$ 195	$ 185
Treasury stock, common, shares		8,113,000	12,121,000	9,194,000	7,280,000	6,473,000
Common stock, shares outstanding		399,760,804	404,899,599
Dividends declared, amount per common share		$ 0.17	$ 0.15	$ 0.15	$ 0.13	$ 0.13
Beginning of period
Accelerated Share Repurchases [Line Items]
Common stock, shares outstanding			404,900,000	416,591,000	425,752,000	432,691,000	437,054,000
End of period
Accelerated Share Repurchases [Line Items]
Common stock, shares outstanding		399,761,000	404,900,000	416,591,000	425,752,000	432,691,000
Subsequent event
Accelerated Share Repurchases [Line Items]
Dividends declared, amount per common share	$ 0.17
Current period
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount		$ 1,000
Future period
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount		$ 1,250
Increase (decrease) in share repurchase program		25.00%