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

[1] The consolidated balance sheet at December 31, 2019 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.