Other Operating Gains (Losses), Net - Summary of Other Operating Gains (Losses), Net by Business Segment (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	1 Months Ended			12 Months Ended
	Jan. 17, 2012	Oct. 13, 2011	Aug. 31, 2011	Dec. 31, 2010	Jul. 31, 2011	Jul. 31, 2012	Feb. 15, 2011
Income Statement [Abstract]
Payment for settlement of disputes to T-Mobile		$ 10
Legal fees incurred with T-Mobile						1.0
Payment received on bankruptcy settlement	1.8
Payment received for termination of agreement				14.4
Damages awarded by court							9.1
Damages awarded for alleging infringement of patents			10.1
Legal fees incurred for law suit			0.7
Proceeds on insurance related to water damage					3.5
Estimated carrying value of damaged building and improvements					1.1
Gain on insurance claim					$ 2.6