Subsequent Events (Details)	1 Months Ended		9 Months Ended
	Oct. 31, 2020 GBP (£)	Oct. 31, 2020 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Oct. 31, 2020 GBP (£)
Subsequent Event [Line Items]
Proceeds issuance of notes			$ 972,766,000	$ 895,774,000
Unsecured debt | Revolving credit facility
Subsequent Event [Line Items]
Credit facility capacity			$ 3,000,000,000.0
Subsequent event
Subsequent Event [Line Items]
Common stock dividend declared (in dollars per share) | $ / shares		$ 0.234
Subsequent event | Notes payable | 1.625% notes, issued in October 2020 and due in December 2030
Subsequent Event [Line Items]
Face amount of notes | £					£ 400,000,000
Stated interest rate (as a percent)		1.625%			1.625%
Price of par value (as a percent)		99.191%			99.191%
Effective yield (as a percent)		1.712%			1.712%
Proceeds issuance of notes | £	£ 396,800,000
Subsequent event | Unsecured debt | Revolving credit facility
Subsequent Event [Line Items]
Credit facility capacity		$ 3,000,000,000.0