Wireless Licenses Goodwill and Other Intangible Assets - Additional Information (Detail) (USD $) In Billions, unless otherwise specified	1 Months Ended
	Jan. 25, 2013 AT&T Amount Expected To Be Received Upon Closing	Jan. 25, 2013 Investment Firm Amount Expected To Be Received Upon Closing	Mar. 31, 2013 License Exchange Transactions	Mar. 31, 2013 Wireless Licenses
Wireless Licenses, Goodwill and Other Intangible Assets [Line Items]
Assets Held-for-sale, Current				$ 2.3
Acquisitions			0.5
License purchase and exchange transactions, net cash proceeds	1.9	0.2
Wireless licenses under development				$ 7.7