Quarterly Financial Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Quarterly Financial Information [Abstract]
Net Revenues | $	$ 1,691	$ 1,597	$ 1,566	$ 1,526	$ 1,551	$ 1,551	$ 1,478	$ 1,478	$ 6,380	$ 6,058	$ 5,435
Expenses Excluding Interest | $	1,046	1,014	999	1,042	997	1,033	957	956	4,101	3,943	3,730
Net Income | $	416	376	353	302	350	321	324	326	1,447	1,321	1,071
Net Income Available to Common Stockholders | $	$ 378	$ 365	$ 330	$ 291	$ 329	$ 312	$ 302	$ 318	$ 1,364	$ 1,261	$ 1,010
Weighted Average Common Shares Outstanding - Basic | shares	1,319	1,316	1,314	1,312	1,309	1,304	1,302	1,299	1,315	1,303	1,285
Weighted Average Common Shares Outstanding - Diluted | shares	1,330	1,328	1,326	1,323	1,320	1,316	1,313	1,311	1,327	1,315	1,293
Earnings Per Common Share: Basic	$ 0.29	$ 0.28	$ 0.25	$ 0.22	$ 0.25	$ 0.24	$ 0.23	$ 0.24	$ 1.04	$ 0.96	$ 0.78
Earnings Per Common Share: Diluted	0.28	0.28	0.25	0.22	0.25	0.24	0.23	0.24	1.03	0.95	0.78
Dividends Declared Per Common Share	0.06	0.06	0.06	0.06	0.06	0.06	0.06	0.06	$ 0.24	$ 0.24	$ 0.24
Range of Common Stock Price Per Share:
High	34.52	35.72	33.78	31.73	30.89	31.00	28.04	29.13
Low	$ 26.40	$ 27.10	$ 29.12	$ 25.43	$ 23.35	$ 26.44	$ 24.56	$ 23.56
Range of Price/Earnings Ratio:
High	34	36	35	34	32	33	30	33
Low	26	27	30	27	24	28	27	27