Common Stock (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Class of Stock [Line Items]
Treasury stock acquired (shares)	5,735,644	10,042,488	7,506,399	12,851,249
Value of treasury stock shares repurchased/withheld	$ 1,664	$ 3,328	$ 2,281	$ 4,223
Remaining authorized repurchase amount	$ 786		$ 786
Treasury Stock Acquired - Share buybacks
Class of Stock [Line Items]
Treasury stock acquired (shares)	5,710,247	9,953,269	7,303,293	12,418,839
Value of treasury stock shares repurchased/withheld	$ 1,657	$ 3,299	$ 2,213	$ 4,098
Treasury Stock Acquired - Income tax withholding
Class of Stock [Line Items]
Treasury stock acquired (shares)	23,645	87,828	196,691	391,865
Value of treasury stock shares repurchased/withheld	$ 7	$ 29	$ 68	$ 125
Treasury Stock Acquired - Exercise cost
Class of Stock [Line Items]
Treasury stock acquired (shares)	1,752	1,391	6,415	40,545