Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Apr. 14, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016
Accelerated Share Repurchases [Line Items]
Treasury Stock, Common, Value	$ 185	$ 190	$ 190	$ 204		$ 169	$ 167	$ 159
Treasury Stock, Common, Shares	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 Payable, Amount Per Share	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Beginning of Period [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding		437,054,000	443,796,000	452,292,000		462,193,000	467,000,000	475,470,000	483,753,000
End of Period [Member]
Accelerated Share Repurchases [Line Items]
Common Stock, Shares, Outstanding	432,690,882	437,054,000	443,796,000	452,292,000		462,193,000	467,000,000	475,470,000