Equity - Stock Repurchases (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 04, 2013
Share repurchases
Average price paid per share (USD per share)		$ 197.21	$ 147.74	$ 113.36
Total cash utilized		$ 1,660	$ 1,006	$ 1,097
Stock repurchased during period (shares)	300,000
Stock repurchased during period	$ 26
Cash used to repurchase treasury shares		$ 1,660	$ 1,001	$ 1,123
2013 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program number of shares authorized to be repurchased (shares)					50,000,000
Maximum number of shares authorized for repurchase under stock repurchase plan as percentage of outstanding common stock (as a percent)					18.00%
Share repurchases
Total number of shares purchased (shares)		8,400,000	6,800,000	9,700,000
Remaining shares available under repurchase program (shares)		10,600,000
Stock Repurchases
Share repurchases
Total cash utilized		$ 1,660	$ 1,001	$ 1,097