Fair Value Measurements - Summary of Fair Values Principal Values and Carrying Values of Company's Debt Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	$ 6,478.5	$ 3,952.0
Fair Value [Member] | 1.875% Convertible Senior Notes due 2013 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	714.1	605.2
Fair Value [Member] | 4.0% Convertible Senior Notes due 2014 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	1,060.6	761.6
Fair Value [Member] | 8.0% Senior Notes due 2016 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument		405.0
Fair Value [Member] | 8.25% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	272.4	407.8
Fair Value [Member] | 5.625% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	523.8
Fair Value [Member] | 5.75% Senior Notes due 2020 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	848.0
Fair Value [Member] | 4.254% 2010-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	713.6	699.0
Fair Value [Member] | 5.101% 2010-2 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	621.4	579.0
Fair Value [Member] | 2.933% 2012-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	635.6
Fair Value [Member] | Revolving Credit Facility [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	100.0
Fair Value [Member] | 2011 Term Loan B [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	493.7	494.4
Fair Value [Member] | 2012-1 Term Loan A [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	194.5
Fair Value [Member] | 2012-2 Term Loan [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	300.8
Principal Balance [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	5,440.1	3,512.5
Principal Balance [Member] | 1.875% Convertible Senior Notes due 2013 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	468.8	535.0
Principal Balance [Member] | 4.0% Convertible Senior Notes due 2014 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	500.0	500.0
Principal Balance [Member] | 8.0% Senior Notes due 2016 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument		375.0
Principal Balance [Member] | 8.25% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	243.8	375.0
Principal Balance [Member] | 5.625% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	500.0
Principal Balance [Member] | 5.75% Senior Notes due 2020 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	800.0
Principal Balance [Member] | 4.254% 2010-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	680.0	680.0
Principal Balance [Member] | 5.101% 2010-2 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	550.0	550.0
Principal Balance [Member] | 2.933% 2012-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	610.0
Principal Balance [Member] | Revolving Credit Facility [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	100.0
Principal Balance [Member] | 2011 Term Loan B [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	492.5	497.5
Principal Balance [Member] | 2012-1 Term Loan A [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	195.0
Principal Balance [Member] | 2012-2 Term Loan [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	300.0
Carrying Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	5,356.2	3,354.5
Carrying Value [Member] | 1.875% Convertible Senior Notes due 2013 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	457.4	485.0
Carrying Value [Member] | 4.0% Convertible Senior Notes due 2014 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	430.8	397.6
Carrying Value [Member] | 8.0% Senior Notes due 2016 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument		373.2
Carrying Value [Member] | 8.25% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	242.2	372.4
Carrying Value [Member] | 5.625% Senior Notes due 2019 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	500.0
Carrying Value [Member] | 5.75% Senior Notes due 2020 [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	800.0
Carrying Value [Member] | 4.254% 2010-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	680.0	680.0
Carrying Value [Member] | 5.101% 2010-2 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	550.0	550.0
Carrying Value [Member] | 2.933% 2012-1 Tower Securities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	610.0
Carrying Value [Member] | Revolving Credit Facility [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	100.0
Carrying Value [Member] | 2011 Term Loan B [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	491.5	496.3
Carrying Value [Member] | 2012-1 Term Loan A [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	195.0
Carrying Value [Member] | 2012-2 Term Loan [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Debt instrument	$ 299.3