Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 09, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016
Accelerated Share Repurchases [Line Items]
Treasury Stock, common, amount		$ 250	$ 195	$ 185	$ 190	$ 190	$ 204	$ 169	$ 167	$ 159
Treasury Stock, common, shares		9,194,000	7,280,000	6,473,000	7,033,000	8,507,000	10,485,000	8,097,000	8,745,000	8,298,000
Common stock, shares, outstanding					437,053,936
Dividends declared, amount per common share		$ 0.15	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Beginning of period
Accelerated Share Repurchases [Line Items]
Common stock, shares, outstanding			425,752,000	432,691,000	437,054,000	443,796,000	452,292,000	462,193,000	467,000,000	475,470,000	483,753,000
End of period
Accelerated Share Repurchases [Line Items]
Common stock, shares, outstanding		416,590,508	425,752,000	432,691,000	437,054,000	443,796,000	452,292,000	462,193,000	467,000,000	475,470,000
Subsequent event
Accelerated Share Repurchases [Line Items]
Dividends declared, amount per common share	$ 0.15