Employee Incentive Plans - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Incentive Plan Aggregate Disclosures [Line Items]
Compensation cost	$ 128	$ 111	$ 101
Employee Stock Option [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Compensation cost	$ 53	$ 42	$ 36
Black-Scholes option-pricing model assumptions and resulting fair value of options [Abstract]
Dividend Yield	0.00%	0.00%	0.10%
Expected Volatility	35.00%	35.00%	35.00%
Risk-free Interest Rate	1.20%	1.30%	1.30%
Expected Option Life	4 years 3 months 18 days	4 years 3 months 18 days	4 years 3 months 18 days
Weighted average fair value of options	$ 42.01	$ 36.40	$ 23.56
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding - January 1	6,433	7,331	7,350
Options Granted	1,336	1,410	2,012
Options Exercised	(577)	(2,146)	(1,869)
Options Expired or canceled	(95)	(162)	(162)
Options outstanding - December 31	7,097	6,433	7,331
Options Exercisable - Number (in thousands)				4,409	3,414	3,919
Share Based Compensation Arrangement By Share Based Payment Award, Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price - Options Outstanding - January 1	$ 68.86	$ 51.84	$ 42.24
Weighted Average Exercise Price - Options Granted	139.20	120.94	78.11
Weighted Average Exercise Price - Options Exercised	62.09	43.63	41.29
Weighted Average Exercise Price - Options Expired or canceled	117.18	86.04	64.27
Weighted Average Exercise Price - Options Outstanding - December 31	$ 82.01	$ 68.86	$ 51.84
Options Exercisable - Weighted Average Exercise Price				$ 58.36	$ 46.55	$ 38.11
Unrecognized compensation expense related to non-vested share-based awards				$ 37
Period in which compensation expense will be recognized	2 years
Information For Stock Options Exercised Details [Abstract]
Intrinsic value of options exercised	$ 41	$ 179	$ 84
Cash received for options exercised	$ 36	$ 94	$ 76
Information for Outstanding Common Stock Options [Abstract]
Options Outstanding - Number (in thousands)	7,097	6,433	7,350	7,097	6,433	7,331
Options Outstanding - Total intrinsic value				$ 372
Options Outstanding - Weighted Average Exercise Price	$ 68.86	$ 68.86	$ 42.24	$ 82.01	$ 68.86	$ 51.84
Options Outstanding - Weighted average remaining contractual life	6 years 6 months
Options Exercisable - Number (in thousands)				4,409	3,414	3,919
Options Exercisable - Total Intrinsic Value				$ 331
Options Exercisable - Weighted Average Exercise Price				$ 58.36	$ 46.55	$ 38.11
Options Exercisable - Weighted Average Remaining Contractual Life	5 years 3 months 18 days
Employee Stock Option [Member] | Minimum [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Award vesting period	1 year
Employee Stock Option [Member] | Maximum [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Award vesting period	5 years
Award expiration period	10 years
Black-Scholes option-pricing model assumptions and resulting fair value of options [Abstract]
Remaining maturity of traded options	1 year