Stock-Based Compensation (Details 9) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended	0 Months Ended		1 Months Ended	0 Months Ended		1 Months Ended	12 Months Ended										1 Months Ended		12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Dec. 28, 2012 Class A common stock	Dec. 02, 2011 Class A common stock	Dec. 31, 2009 Class A common stock	Dec. 28, 2012 Class B common stock	Dec. 02, 2011 Class B common stock	Dec. 31, 2009 Class B common stock	Dec. 31, 2012 Stock options	Dec. 31, 2011 Stock options	Dec. 31, 2010 Stock options	Dec. 31, 2012 Stock options Maximum	Dec. 31, 2011 Stock options Maximum	Dec. 31, 2010 Stock options Maximum	Dec. 31, 2012 Stock options Minimum	Dec. 31, 2011 Stock options Minimum	Dec. 31, 2010 Stock options Minimum	Dec. 31, 2012 Stock option adjustment	Jan. 31, 2012 Stock option adjustment 2012	Feb. 28, 2010 Stock option adjustment 2009	Dec. 31, 2012 Stock option adjustment 2009	Dec. 31, 2010 Stock option adjustment 2009
Black-Scholes option valuation model, assumptions
Risk free interest rate, low end of range (as a percent)									0.41%	0.36%	1.50%
Risk free interest rate, high end of range (as a percent)									1.29%	3.18%	2.89%
Volatility factor, low end of range (as a percent)									33.15%	31.74%	33.33%
Volatility factor, high end of range (as a percent)									39.50%	45.56%	38.63%
Expected term of options												5 years 10 months 24 days	10 years	7 years 6 months	3 years 1 month 6 days	3 years 7 months 6 days	5 years 2 months 12 days
Weighted-average fair value of options granted (in dollars per share)												$ 13.79	$ 14.77	$ 8.14	$ 6.72	$ 8.73	$ 6.83
Dividend in cash per share			$ 1.00	$ 2.00	$ 2.00	$ 1.00	$ 2.00	$ 2.00
Reduction in exercise price due to dividend declaration (in dollars per share)																			$ 2.00	$ 2.00
Threshold for reduction in exercise price due to dividend declaration (in dollars per share)																		$ 1.00
Decrease in exercise price due to stock option adjustment (in dollars per share)																		$ 0.77
Additional non-cash stock-based compensation cost in connection with Stock Option Adjustment																		$ 23.0
Adjustment to recognized non-cash, stock-based compensation expense	5	8
Adjustment to recognized non-cash, stock-based compensation expense to be expensed over the remaining vesting period		$ 3																			$ 14	$ 3