Quarterly Financial Information (Schedule of Quarterly Financial Information) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares	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, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Quarterly Financial Information [Abstract]
Net Revenues | $	$ 1,972	$ 1,914	$ 1,828	$ 1,764	$ 1,691	$ 1,597	$ 1,566	$ 1,526	$ 7,478	$ 6,380	$ 6,058
Expenses Excluding Interest | $	1,148	1,120	1,108	1,109	1,046	1,014	999	1,042	4,485	4,101	3,943
Net Income | $	522	503	452	412	416	376	353	302	1,889	1,447	1,321
Net Income Available to Common Stockholders | $	$ 478	$ 470	$ 406	$ 392	$ 378	$ 365	$ 330	$ 291	$ 1,746	$ 1,364	$ 1,261
Weighted Average Common Shares Outstanding - Basic | shares	1,329	1,324	1,322	1,321	1,319	1,316	1,314	1,312	1,324	1,315	1,303
Weighted Average Common Shares Outstanding - Diluted | shares	1,341	1,334	1,333	1,330	1,330	1,328	1,326	1,323	1,334	1,327	1,315
Basic	$ 0.36	$ 0.36	$ 0.31	$ 0.30	$ 0.29	$ 0.28	$ 0.25	$ 0.22	$ 1.32	$ 1.04	$ 0.96
Diluted	0.36	0.35	0.30	0.29	0.28	0.28	0.25	0.22	1.31	1.03	0.95
Dividends Declared Per Common Share	0.07	0.07	0.07	0.06	0.06	0.06	0.06	0.06	$ 0.27	$ 0.24	$ 0.24
Range of Common Stock Price Per Share:
High	40.58	31.87	31.07	32.23	34.52	35.72	33.78	31.73
Low	$ 30.66	$ 23.83	$ 24.02	$ 21.51	$ 26.40	$ 27.10	$ 29.12	$ 25.43
Range of Price/Earnings Ratio:
High	31	26	27	29	34	36	35	34
Low	24	20	21	20	26	27	30	27