Other Financial Statement Disclosures - Long Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2016	Apr. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total carrying value	$ 2,645.6			$ 2,692.4
Current portion of long-term debt	357.1			0.0
Carrying value, less current portion	2,288.5			2,692.4
Senior Notes [Member] | 5% Senior Notes, due September 2017 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 357.1			$ 365.5
Stated rate	5.00%	5.00%	5.00%	5.00%
Principal amount	$ 357.7			$ 366.6
Effective rate	5.20%			5.20%
Senior Notes [Member] | 7.875% Senior Notes, due August 2019 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 394.7			$ 432.9
Stated rate	7.875%	7.875%	7.875%	7.875%
Principal amount	$ 396.5			$ 435.5
Effective rate	8.00%			8.00%
Senior Notes [Member] | 4.875% Senior Notes, due June 2022 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 705.5			$ 706.2
Stated rate	4.875%			4.875%
Principal amount	$ 700.0			$ 700.0
Effective rate	4.70%			4.70%
Senior Notes [Member] | 4.75% Senior Notes, due January 2024 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 397.3			$ 397.1
Stated rate	4.75%			4.75%
Principal amount	$ 400.0			$ 400.0
Effective rate	4.80%			4.80%
Senior Notes [Member] | 5.4% Senior Notes due, December 2042 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 394.9			$ 394.7
Stated rate	5.40%			5.40%
Principal amount	$ 400.0			$ 400.0
Effective rate	5.40%			5.40%
Senior Notes [Member] | 5.85% Senior Notes, due January 2044 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 396.1			$ 396.0
Stated rate	5.85%			5.85%
Principal amount	$ 400.0			$ 400.0
Effective rate	5.90%			5.90%