Other Financial Statement Disclosures - Long Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Jan. 09, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total carrying value	$ 2,510.2		$ 2,680.2
Current portion of long-term debt	0.0		126.8
Carrying value, less current portion	2,510.2		2,553.4
Subject Notes [Member] | 5% Senior Notes, due September 2017 [Member]
Debt Instrument [Line Items]
Total carrying value	0.0		$ 92.0
Stated rate			5.00%
Principal amount		$ 92.1	$ 92.2
Effective rate			5.20%
Subject Notes [Member] | 7.875% Senior Notes, due August 2019 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 200.8		$ 208.9
Stated rate	7.875%		7.875%
Principal amount	$ 201.4		$ 209.8
Effective rate	8.00%		8.00%
Subject Notes [Member] | 4.875% Senior Notes, due June 2022 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 624.8		$ 695.4
Stated rate	4.875%		4.875%
Principal amount	$ 620.8		$ 690.2
Effective rate	4.70%		4.70%
Subject Notes [Member] | 4.75% Senior Notes, due January 2024 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 395.8		$ 395.6
Stated rate	4.75%		4.75%
Principal amount	$ 398.1		$ 398.1
Effective rate	4.80%		4.80%
Subject Notes [Member] | 7.375% Senior Note Payable Due June 2025 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 497.4		$ 497.2
Stated rate	7.375%		7.375%
Principal amount	$ 500.0		$ 500.0
Effective rate	7.40%		7.40%
Subject Notes [Member] | 5.4% Senior Notes due, December 2042 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 395.1		$ 394.9
Stated rate	5.40%		5.40%
Principal amount	$ 400.0		$ 400.0
Effective rate	5.40%		5.40%
Subject Notes [Member] | 5.85% Senior Notes, due January 2044 [Member]
Debt Instrument [Line Items]
Total carrying value	$ 396.3		$ 396.2
Stated rate	5.85%		5.85%
Principal amount	$ 400.0		$ 400.0
Effective rate	5.90%		5.90%