Debt (Secured Tower Revenue Securities Series 2010) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Tower Revenue Securities issued				$ 1,212,381,000
4.254% Secured Tower Revenue Securities Series 2010-1 [Member]
Tower Revenue Securities issued			680,000,000
Tower Revenue Securities, annual interest rate			4.254%
Tower Revenue Securities anticipated repayment date			April 16, 2015
Tower Revenue Securities maturity date			April 16, 2040
5.101% Secured Tower Revenue Securities Series 2010-2 [Member]
Tower Revenue Securities issued			550,000,000
Tower Revenue Securities, annual interest rate			5.101%
Tower Revenue Securities anticipated repayment date			April 16, 2017
Tower Revenue Securities maturity date			April 16, 2042
Tower Securities [Member]
Weighted average annual fixed coupon interest rate	4.60%		4.60%
Interest expense on 2010 Tower Revenue Securities	$ 14,300,000	$ 12,000,000	$ 28,700,000	$ 12,000,000