Employee Incentive Plans - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Incentive Plan Aggregate Disclosures [Line Items]
Compensation cost	$ 180	$ 178	$ 128
Employee Stock Option [Member]
Black-Scholes option-pricing model assumptions and resulting fair value of options [Abstract]
Dividend Yield	0.00%	0.00%	0.00%
Expected volatility	35.00%	35.00%	35.00%
Risk-free interest rate	2.50%	1.80%	1.20%
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	$ 64.18	$ 46.38	$ 42.01
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding - January 1	6,156	7,097	6,433
Options Granted	7,080	1,230	1,336
Options Exercised	(771)	(2,072)	(577)
Options Expired or canceled	(95)	(99)	(95)
Options outstanding - December 31	12,370	6,156	7,097
Options Exercisable - Number (in thousands)				9,446	3,894	4,409
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	$ 100.79	$ 82.01	$ 68.86
Weighted Average Exercise Price - Options Granted	143.62	149.17	139.2
Weighted Average Exercise Price - Options Exercised	88.35	63.41	62.09
Weighted Average Exercise Price - Options Expired or canceled	165.04	138.41	117.18
Weighted Average Exercise Price - Options Outstanding - December 31	$ 125.46	$ 100.79	$ 82.01
Options Exercisable - Weighted Average Exercise Price				$ 114.22	$ 77.36	$ 58.36
Related compensation expense to be recognized				$ 61
Period over which compensation expense will be recognized	2 years
Information For Stock Options Exercised Details [Abstract]
Intrinsic value of options exercised	$ 86	$ 218	$ 41
Cash received for options exercised	68	131	36
Tax benefit from options exercised	$ 8	$ 41	$ 11
Information for Outstanding Common Stock Options [Abstract]
Options Outstanding - Number (in thousands)	12,370	6,156	6,433	12,370	6,156	7,097
Options Outstanding - Total intrinsic value				$ 804
Options Outstanding - Weighted Average Exercise Price	$ 100.79	$ 100.79	$ 68.86	$ 125.46	$ 100.79	$ 82.01
Options Outstanding - Weighted average remaining contractual life	5 years 4 months 24 days
Options Exercisable - Number (in thousands)				9,446	3,894	4,409
Options Exercisable - Total Intrinsic Value				$ 715
Options Exercisable - Weighted Average Exercise Price				$ 114.22	$ 77.36	$ 58.36
Options Exercisable - Weighted Average Remaining Contractual Life	4 years 6 months
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	3 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