Derivative Instruments and Hedging Activities (Interest Rate Swap Contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Aug. 31, 2015
Derivative [Line Items]
Notional amount	$ 9,275.0
Interest rate swaps
Derivative [Line Items]
Notional amount	3,550.0	$ 2,700.0
Interest rate swaps | Designated as hedging instruments
Derivative [Line Items]
Proceeds from settlement of interest rate swap contracts	$ 10.8	25.5
2.450% senior notes due 2015
Derivative [Line Items]
Interest rate (as a percent)	2.45%
3.875% senior notes due 2025
Derivative [Line Items]
Interest rate (as a percent)			3.875%
Senior Notes | 2.450% senior notes due 2015 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 0.0	$ 300.0
Interest rate (as a percent)	2.45%
Senior Notes | 1.900% senior notes due 2017
Derivative [Line Items]
Interest rate (as a percent)	1.90%	1.90%
Senior Notes | 1.900% senior notes due 2017 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 300.0	$ 300.0
Interest rate (as a percent)	1.90%
Senior Notes | 2.300% senior notes due 2018
Derivative [Line Items]
Interest rate (as a percent)	2.30%	2.30%
Senior Notes | 2.300% senior notes due 2018 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 200.0	$ 200.0
Interest rate (as a percent)	2.30%
Senior Notes | 2.250% senior notes due 2019
Derivative [Line Items]
Interest rate (as a percent)	2.25%	2.25%
Senior Notes | 2.250% senior notes due 2019 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 500.0	$ 500.0
Interest rate (as a percent)	2.25%
Senior Notes | 3.950% senior notes due 2020
Derivative [Line Items]
Interest rate (as a percent)	3.95%	3.95%
Senior Notes | 3.950% senior notes due 2020 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 500.0	$ 500.0
Interest rate (as a percent)	3.95%
Senior Notes | 3.250% senior notes due 2022
Derivative [Line Items]
Interest rate (as a percent)	3.25%
Senior Notes | 3.250% senior notes due 2022 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 1,000.0	$ 750.0
Interest rate (as a percent)	3.25%
Senior Notes | 4.000% senior notes due 2023
Derivative [Line Items]
Interest rate (as a percent)	4.00%	4.00%
Senior Notes | 4.000% senior notes due 2023 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 700.0	$ 150.0
Interest rate (as a percent)	4.00%
Senior Notes | 3.625% senior notes due 2024
Derivative [Line Items]
Interest rate (as a percent)	3.625%	3.625%
Senior Notes | 3.625% senior notes due 2024 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 100.0	$ 0.0
Interest rate (as a percent)	3.625%
Senior Notes | 3.875% senior notes due 2025
Derivative [Line Items]
Interest rate (as a percent)	3.875%
Senior Notes | 3.875% senior notes due 2025 | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 250.0	$ 0.0
Interest rate (as a percent)	3.875%