Stockholders' Equity (Schedule of Share Repurchase Authorizations) (Details) - Class A Common Stock - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended			13 Months Ended	25 Months Ended	37 Months Ended	47 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 06, 2016	Dec. 08, 2015	Dec. 02, 2014	Dec. 10, 2013	Feb. 05, 2013
Class of Stock [Line Items]
Board Authorization	$ 17,250			$ 17,250	$ 17,250	$ 17,250	$ 17,250
Dollar-value of shares repurchased	3,511	$ 3,518	$ 3,386
Remaining authorization	$ 4,996	$ 4,507	$ 4,025	4,996	4,996	4,996	$ 4,996
Shares repurchased	36.9	38.3	44.5				148.9
Average price paid per share	$ 95.18	$ 91.70	$ 76.14				$ 82.29
February 2013 Share Repurchase Plan
Class of Stock [Line Items]
Board Authorization												$ 2,000
Dollar-value of shares repurchased	$ 0	$ 0	$ 161
Remaining authorization	$ 0	$ 0	$ 0	0	0	0	$ 0
Shares repurchased	0.0	0.0	1.9				31.1
Average price paid per share	$ 0.00	$ 0.00	$ 83.22				$ 64.26
December 2013 Share Repurchase Plan
Class of Stock [Line Items]
Board Authorization											$ 3,500
Dollar-value of shares repurchased	$ 0	$ 275	$ 3,225
Remaining authorization	$ 0	$ 0	$ 275	0	0	$ 0	$ 0
Shares repurchased	0.0	3.2	42.6			45.8
Average price paid per share	$ 0.00	$ 84.31	$ 75.81			$ 76.42
December 2014 Share Repurchase Plan
Class of Stock [Line Items]
Board Authorization										$ 3,750
Dollar-value of shares repurchased	$ 507	$ 3,243	$ 0
Remaining authorization	$ 0	$ 507	$ 3,750	0	$ 0	$ 0	0
Shares repurchased	5.7	35.1	0.0		40.8
Average price paid per share	$ 89.76	$ 92.39	$ 0.00		$ 92.03
December 2015 Share Repurchase Plan
Class of Stock [Line Items]
Board Authorization									$ 4,000
Dollar-value of shares repurchased	$ 3,004	$ 0
Remaining authorization	$ 996	$ 4,000		$ 996	$ 996	996	996
Shares repurchased	31.2	0.0		31.2
Average price paid per share	$ 96.15	$ 0.00		$ 96.15
December 2016 Share Repurchase Plan
Class of Stock [Line Items]
Board Authorization								$ 4,000
Remaining authorization	$ 4,000			$ 4,000	$ 4,000	$ 4,000	$ 4,000
Shares repurchased	0.0
Average price paid per share	$ 0.00