Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended				12 Months Ended
	May 20, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 02, 2012 Mobilitie [Member]	Oct. 31, 2012 TowerCo [Member]	Dec. 31, 2012 Common stock equivalents 1.875% Notes [Member]	Dec. 31, 2012 Common stock equivalents 4.0% Notes [Member]	Dec. 31, 2012 Class A Common Stock [Member]	Mar. 07, 2012 Class A Common Stock [Member]	Apr. 27, 2011 Class A Common Stock [Member]	Dec. 31, 2007 Class A Common Stock [Member]
Class of Stock [Line Items]
Interest rate for senior notes			1.875%				1.875%	4.00%
Stock repurchase authorized		$ 150.0									$ 300.0
Common stock shares repurchased and retired			5,917,940	3,174,385
Common stock repurchased and retired values			225.1	107.4
Commissions and fees			75.1
New stock repurchase authorized program		300.0
Shares registered for Performance and Equity Incentive Plan	15,000,000
Shares, issued												4,000,000
Shares reclassified as authorized and unissued									1,700,000
Common stock, shares issued		126,933,000	126,933,000							6,005,000
Common stock value per share										$ 47.30
Proceeds from sale of stock, net of related fees										283.9
Total consideration paid in cash					$ 850.0	$ 1,200.0
Newly issued shares					5,250,000	4,588,840