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Risk Management and Use of Derivative Financial Instruments - Narratives (Details) ¥ in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) offering	Sep. 30, 2018 USD ($)	Sep. 30, 2019 JPY (¥)	Sep. 30, 2019 EUR (€)	Sep. 19, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary of Derivative Instruments
Net collateral posted for derivatives	$ 0		$ 0					$ 0
Derivative, remaining maturity			77 months
Total credit exposure on derivatives	38,500,000		$ 38,500,000
Derivatives, net liability position	11,000,000.0		11,000,000.0					7,300,000
Aggregate termination value for immediate settlement	11,200,000		11,200,000					7,600,000
Other comprehensive income foreign currency gain (loss)	108,800,000	$ 10,500,000	122,300,000	$ 55,000,000.0
Unsecured revolving credit facility
Summary of Derivative Instruments
Debt	22,410,000		22,410,000					91,563,000
EUR \| Unsecured revolving credit facility
Summary of Derivative Instruments
Debt	0		0					69,273,000
JPY \| Unsecured revolving credit facility
Summary of Derivative Instruments
Debt	22,410,000		$ 22,410,000		¥ 2.4			$ 22,290,000
Unsecured senior notes
Summary of Derivative Instruments
Number Of Offerings Completed \| offering			5
Principal amount	$ 4,300,000,000		$ 4,300,000,000
Unsecured senior notes \| 2.0% Senior Notes due 2023
Summary of Derivative Instruments
Principal amount \| €						€ 500,000,000.0
Coupon rate (percentage)	2.00%		2.00%		2.00%	2.00%
Unsecured senior notes \| 2.25% Senior Notes due 2024
Summary of Derivative Instruments
Principal amount \| €						€ 500,000,000.0
Coupon rate (percentage)	2.25%		2.25%		2.25%	2.25%
Unsecured senior notes \| 2.250% Senior Notes due 2026
Summary of Derivative Instruments
Principal amount \| €						€ 500,000,000.0
Coupon rate (percentage)	2.25%		2.25%		2.25%	2.25%
Unsecured senior notes \| 2.125% Senior Notes due 2027
Summary of Derivative Instruments
Principal amount \| €						€ 500,000,000.0
Coupon rate (percentage)	2.125%		2.125%		2.125%	2.125%
Unsecured senior notes \| 1.350% Senior Notes due 2028
Summary of Derivative Instruments
Principal amount						€ 500,000,000.0	$ 500,000,000.0
Coupon rate (percentage)	1.35%		1.35%		1.35%	1.35%	1.35%
Individual Counterparty
Summary of Derivative Instruments
Total credit exposure on derivatives	$ 13,300,000		$ 13,300,000
Interest expense
Summary of Derivative Instruments
Estimated amount reclassified from OCI to expense (gain)			2,000,000.0
Other gains
Summary of Derivative Instruments
Estimated amount reclassified from OCI to expense (gain)			$ (16,000,000.0)