Derivative Instruments and Hedging Activities (Forward Starting Interest Rate Swaps) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
2.450% senior notes due 2015
Derivative [Line Items]
Interest rate (as a percentage)	2.45%
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%
Senior notes | 2.450% senior notes due 2015
Derivative [Line Items]
Interest rate (as a percentage)	2.45%
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 | 3.630% senior notes due 2024
Derivative [Line Items]
Interest rate (as a percentage)	3.625%
Fair value hedges | Designated as hedging instruments | Interest rate swap contracts
Derivative [Line Items]
Notional amount	$ 3,600.0	$ 2,700.0
Fair value hedges | Senior notes | Designated as hedging instruments | 2.450% senior notes due 2015 | Interest rate swap contracts
Derivative [Line Items]
Notional amount	300.0	300.0
Fair value hedges | Senior notes | Designated as hedging instruments | 1.900% senior notes due 2017 | Interest rate swap contracts
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 contracts
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 contracts
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 contracts
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 contracts
Derivative [Line Items]
Notional amount	1,000.0	750.0
Fair value hedges | Senior notes | Designated as hedging instruments | 4.000% senior notes due 2023 | Interest rate swap contracts
Derivative [Line Items]
Notional amount	700.0	150.0
Fair value hedges | Senior notes | Designated as hedging instruments | 3.630% senior notes due 2024 | Interest rate swap contracts
Derivative [Line Items]
Notional amount	$ 100.0	$ 0.0