Quarterly Financial Information (Unaudited) (Schedule of Quarterly Financial Information) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares	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, 2017 USD ($) $ / shares shares		Dec. 31, 2016 USD ($) $ / shares shares		Dec. 31, 2015 USD ($) $ / shares shares
Quarterly Financial Information Disclosure [Abstract]
Total Net Revenues | $	$ 2,242	$ 2,165	$ 2,130	$ 2,081	$ 1,972	$ 1,914	$ 1,828	$ 1,764	$ 8,618		$ 7,478		$ 6,380
Total Expenses Excluding Interest | $	1,289	1,220	1,221	1,238	1,148	1,120	1,108	1,109	4,968		4,485		4,101
Net Income | $	597	618	575	564	522	503	452	412	2,354		1,889		1,447
Net Income Available to Common Stockholders | $	$ 550	$ 575	$ 530	$ 525	$ 478	$ 470	$ 406	$ 392	$ 2,180		$ 1,746		$ 1,364
Weighted Average Common Shares Outstanding - Basic (in shares) | shares	1,343	1,339	1,338	1,336	1,329	1,324	1,322	1,321	1,339		1,324		1,315
Weighted Average Common Shares Outstanding - Diluted (in shares) | shares	1,358	1,353	1,351	1,351	1,341	1,334	1,333	1,330	1,353	[1]	1,334	[1]	1,327	[1]
Basic (USD per share)	$ 0.41	$ 0.43	$ 0.40	$ 0.39	$ 0.36	$ 0.36	$ 0.31	$ 0.30	$ 1.63		$ 1.32		$ 1.04
Diluted (USD per share)	0.41	0.42	0.39	0.39	0.36	0.35	0.30	0.29	1.61		1.31		1.03
Dividends Declared Per Common Share (USD per share)	0.08	0.08	0.08	0.08	0.07	0.07	0.07	0.06	$ 0.32		$ 0.27		$ 0.24
Range of Common Stock Price Per Share:
High (USD per share)	52.52	44.35	44.10	43.65	40.58	31.87	31.07	32.23
Low (USD per share)	$ 42.20	$ 38.06	$ 37.16	$ 37.62	$ 30.66	$ 23.83	$ 24.02	$ 21.51
Range of Price/Earnings Ratio:
High	33	28	30	31	31	26	27	29
Low	26	24	25	27	24	20	21	20

[1] Antidilutive stock options and restricted stock units excluded from the calculation of diluted EPS totaled 15 million, 26 million, and 23 million shares in 2017, 2016, and 2015, respectively.