Debt (Issuance of June 2016 Senior Notes) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Jun. 09, 2016	Dec. 31, 2015		Nov. 09, 2010
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage							6.00%
June 2016 Senior Notes
Debt Instrument [Line Items]
Debt Related Commitment Fees and Debt Issuance Costs		$ 48.7
Senior Notes | 2019 Senior Notes (2.500%)
Debt Instrument [Line Items]
Long-term debt		999.1	[1]	$ 1,000.0	$ 0.0	[1]
Debt instrument, interest rate, stated percentage	[1]			2.50%
Debt Instrument, Unamortized Discount				$ 0.9
Senior Notes | 2021 Senior Notes (3.150%)
Debt Instrument [Line Items]
Long-term debt		2,247.7	[2]	$ 2,250.0	0.0	[2]
Debt instrument, interest rate, stated percentage	[2]			3.15%
Debt Instrument, Unamortized Discount				$ 2.4
Senior Notes | 2026 Senior Notes (3.950%)
Debt Instrument [Line Items]
Long-term debt		2,233.5	[3]	$ 2,250.0	0.0	[3]
Debt instrument, interest rate, stated percentage	[3]			3.95%
Debt Instrument, Unamortized Discount				$ 16.5
Senior Notes | 2046 Senior Notes (5.250%)
Debt Instrument [Line Items]
Long-term debt		$ 999.8	[4]	$ 1,000.0	$ 0.0	[4]
Debt instrument, interest rate, stated percentage	[4]			5.25%
Debt Instrument, Unamortized Discount				$ 0.2

[1] Instrument is callable by the Company at any time at the greater of 100% of the principal amount and the sum of the present values of the remaining scheduled payments of principal and interest discounted at the U.S. Treasury rate plus 0.25% plus, in each case, accrued and unpaid interest.

[2] Instrument is callable by the Company at any time prior to the date that is one month prior to the instrument’s maturity date at the greater of 100% of the principal amount and the sum of the present values of the remaining scheduled payments of principal and interest discounted at the U.S. Treasury rate plus 0.30% plus, in each case, accrued and unpaid interest. On or after such date, the instrument is callable by the Company at 100% of the principal amount plus accrued and unpaid interest.

[3] Instrument is callable by the Company at any time prior to the date that is three months prior to the instrument’s maturity date at the greater of 100% of the principal amount and the sum of the present values of the remaining scheduled payments of principal and interest discounted at the U.S. Treasury rate plus 0.35% plus, in each case, accrued and unpaid interest. On or after such date, the instrument is callable by the Company at 100% of the principal amount plus accrued and unpaid interest.

[4] Instrument is callable by the Company at any time prior to the date that is six months prior to the instrument’s maturity date at the greater of 100% of the principal amount and the sum of the present values of the remaining scheduled payments of principal and interest discounted at the U.S. Treasury rate plus 0.40% plus, in each case, accrued and unpaid interest. On or after such date, the instrument is callable by the Company at 100% of the principal amount plus accrued and unpaid interest.