Derivative Instruments and Hedging Activities (Forward Starting Interest Rate Swaps) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
1.900% senior notes due 2017
Derivative [Line Items]
Interest rate (as a percentage)	1.90%
3.950% senior notes due 2020
Derivative [Line Items]
Interest rate (as a percentage)	3.95%
3.250% senior notes due 2022
Derivative [Line Items]
Interest rate (as a percentage)	3.25%
4.000% senior notes due 2023
Derivative [Line Items]
Interest rate (as a percentage)	4.00%
3.625% senior notes due 2024
Derivative [Line Items]
Interest rate (as a percentage)	3.625%
3.875% senior notes due 2025
Derivative [Line Items]
Interest rate (as a percentage)	3.875%
Senior notes | 1.900% senior notes due 2017
Derivative [Line Items]
Interest rate (as a percentage)	1.90%
Senior notes | 2.300% senior notes due 2018
Derivative [Line Items]
Interest rate (as a percentage)	2.30%
Senior notes | 2.250% senior notes due 2019
Derivative [Line Items]
Interest rate (as a percentage)	2.25%
Senior notes | 3.950% senior notes due 2020
Derivative [Line Items]
Interest rate (as a percentage)	3.95%
Senior notes | 3.250% senior notes due 2022
Derivative [Line Items]
Interest rate (as a percentage)	3.25%
Senior notes | 4.000% senior notes due 2023
Derivative [Line Items]
Interest rate (as a percentage)	4.00%
Senior notes | 3.625% senior notes due 2024
Derivative [Line Items]
Interest rate (as a percentage)	3.625%
Senior notes | 3.875% senior notes due 2025
Derivative [Line Items]
Interest rate (as a percentage)	3.875%
Fair value hedges | Designated as hedging instruments | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	$ 3,600.0	$ 3,550.0
Fair value hedges | Senior notes | Designated as hedging instruments | 1.900% senior notes due 2017 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	300.0	300.0
Fair value hedges | Senior notes | Designated as hedging instruments | 2.300% senior notes due 2018 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	200.0	200.0
Fair value hedges | Senior notes | Designated as hedging instruments | 2.250% senior notes due 2019 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	500.0	500.0
Fair value hedges | Senior notes | Designated as hedging instruments | 3.950% senior notes due 2020 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	500.0	500.0
Fair value hedges | Senior notes | Designated as hedging instruments | 3.250% senior notes due 2022 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	1,000.0	1,000.0
Fair value hedges | Senior notes | Designated as hedging instruments | 4.000% senior notes due 2023 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	700.0	700.0
Fair value hedges | Senior notes | Designated as hedging instruments | 3.625% senior notes due 2024 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	100.0	100.0
Fair value hedges | Senior notes | Designated as hedging instruments | 3.875% senior notes due 2025 | Interest rate swap agreements
Derivative [Line Items]
Notional Amount	$ 300.0	$ 250.0