Borrowings Under Credit Facilities and Commercial Paper Program - Narrative (Details)	1 Months Ended	9 Months Ended
	Jan. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) term bank	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Number of banks in consortium | bank		31
Borrowings outstanding		$ 0	$ 1,587,597,000
Unsecured revolving credit facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		3,000,000,000
Borrowings outstanding		0
Available to borrow in alternate currencies		$ 1,000,000,000
Facility fee		0.15%
Number of successive terms | term		2
Successive term		6 months
Unsecured revolving credit facility | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		0.825%
Unsecured revolving credit facility | Accordion feature
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		$ 1,000,000,000
Term credit facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		500,000,000
Term credit facility, CAD denominated
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		250,000,000
Term credit facility, CAD denominated | Accordion feature
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		250,000,000
Commercial paper note program
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 1,000,000,000
Borrowings outstanding		$ 0
Commercial paper note program | Maximum
Line of Credit Facility [Line Items]
Debt instrument, term	397 days