Stockholders' Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended		0 Months Ended				1 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 28, 2013 Common stock	Mar. 29, 2013 Common stock	Jun. 29, 2012 Common stock	Mar. 30, 2012 Common stock	Feb. 28, 2013 Common stock	May 31, 2012 Common stock	Feb. 29, 2012 Common stock	Jun. 30, 2013 Common stock	Jun. 30, 2012 Common stock	Jun. 30, 2013 Series A	Dec. 31, 2012 Series A	Jun. 30, 2012 Series A	Dec. 31, 2011 Series A	Jun. 30, 2013 Series B	Dec. 31, 2012 Series B	Jun. 30, 2012 Series B	Dec. 31, 2011 Series B
Quarterly Common Stock Dividend Paid
Dividends to common stockholders	$ 135.2	$ 108.0	$ 67.6	$ 67.6	$ 53.7	$ 54.3
Dividend paid on common stock (in dollars per share)			$ 0.23	$ 0.23	$ 0.18	$ 0.18
Reconciliation of Outstanding Shares
Outstanding shares at beginning of period										293.8	301.1	3.0	3.0	3.0	3.0	10.0	10.0	10.0	10.0
Shares issued										3.0	2.3
Treasury stock acquired										(2.9)	(7.8)
Outstanding shares at end of period										293.9	295.6	3.0	3.0	3.0	3.0	10.0	10.0	10.0	10.0
Common stock share repurchase disclosures
Share repurchase program, maximum authorized amount (in dollars)							$ 150.0	$ 200.0	$ 100.0