Stockholders' Equity (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended		27 Months Ended	1 Months Ended	3 Months Ended		12 Months Ended	27 Months Ended		1 Months Ended	3 Months Ended	12 Months Ended	27 Months Ended	1 Months Ended		3 Months Ended		12 Months Ended		27 Months Ended		1 Months Ended	3 Months Ended		27 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Apr. 28, 2011 Class A Common Stock [Member]	Mar. 31, 2013 Class A Common Stock [Member]	Mar. 31, 2012 Class A Common Stock [Member]	Dec. 31, 2012 Class A Common Stock [Member]	Mar. 31, 2013 Class A Common Stock [Member]	Mar. 31, 2013 Class A Common Stock [Member]	Jun. 30, 2012 2012 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2013 2012 repurchase plan [Member] Class A Common Stock [Member]	Dec. 31, 2012 2012 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2013 2012 repurchase plan [Member] Class A Common Stock [Member]	Apr. 30, 2011 2010 repurchase plan [Member] Class A Common Stock [Member]	Sep. 30, 2010 2010 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2013 2010 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2012 2010 repurchase plan [Member] Class A Common Stock [Member]	Dec. 31, 2012 2010 repurchase plan [Member] Class A Common Stock [Member]	Dec. 31, 2011 2010 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2013 2010 repurchase plan [Member] Class A Common Stock [Member]	Mar. 31, 2013 2010 repurchase plan [Member] Class A Common Stock [Member]	Feb. 28, 2013 2013 Share repurchase plan [Domain] Class A Common Stock [Member]	Apr. 25, 2013 2013 Share repurchase plan [Domain] Class A Common Stock [Member]	Mar. 31, 2013 2013 Share repurchase plan [Domain] Class A Common Stock [Member]	Mar. 31, 2013 2013 Share repurchase plan [Domain] Class A Common Stock [Member]
Class of Stock [Line Items]
Board authorization									$ 5,500,000,000	$ 1,500,000,000					$ 1,000,000,000				$ 2,000,000,000		$ 2,000,000,000	$ 2,000,000,000
Additional amount approved for repurchase				1,000,000,000										1,000,000,000
Shares repurchased during period		0.65				0.65										0					6.54		0.70	0.31
Stock Repurchased During Period, Value																							344,000,000
Dollar value of shares repurchased during period	766,000,000					248,000,000					604,000,000					0	248,000,000							162,000,000
Remaining authorization			$ 1,838,000,000				$ 604,000,000					$ 604,000,000	$ 0					$ 0		$ 0					$ 1,838,000,000
Average price paid per share					$ 518.36			$ 367.34			$ 517.16		$ 481.58			$ 0.00	$ 379.68			$ 305.60			$ 527.57	$ 522.87	$ 522.87
Shares repurchased					1.48			9.96			1.17		3.11												0.31