Notes Payable - General (Details) - Notes and bonds payable	1 Months Ended
	Jan. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 GBP (£)	Jul. 31, 2021 GBP (£)	Dec. 31, 2020 USD ($)	Oct. 31, 2020 GBP (£)	Jul. 31, 2020 USD ($)	May 31, 2020 USD ($)
Debt
Total principal amount		$ 8,353,000,000			$ 8,303,000,000
Unamortized net original issuance premiums and deferred financing costs		(44,000,000)			(35,000,000)
Net payable amount		8,309,000,000			$ 8,268,000,000
3.250% notes, $450 issued in October 2012 and $500 issued in December 2017, both due in October 2022
Debt
Interest rate (as a percent)	3.25%				3.25%
Principal amount		0
Total principal amount		$ 0			$ 950,000,000
Early redemption of notes payable	$ 950,000,000
3.250% notes, issued in October 2012 and due in October 2022
Debt
Principal amount					450,000,000
3.250% notes, issued in December 2017 and due in October 2022
Debt
Principal amount					500,000,000
4.650% notes, issued in July 2013 and due in August 2023
Debt
Interest rate (as a percent)		4.65%	4.65%
Principal amount		$ 750,000,000
Total principal amount		$ 750,000,000			750,000,000
3.875% notes, issued in June 2014 and due in July 2024
Debt
Interest rate (as a percent)		3.875%	3.875%
Principal amount		$ 350,000,000
Total principal amount		$ 350,000,000			350,000,000
3.875% notes, issued in April 2018 and due in April 2025
Debt
Interest rate (as a percent)		3.875%	3.875%
Principal amount		$ 500,000,000
Total principal amount		$ 500,000,000			500,000,000
0.750% notes, issued in December 2020 and due in March 2026
Debt
Interest rate (as a percent)		0.75%	0.75%
Principal amount		$ 325,000,000
Total principal amount		$ 325,000,000			325,000,000
4.125% notes, $250 issued in September 2014 and $400 issued in March 2017, both due in October 2026
Debt
Interest rate (as a percent)		4.125%	4.125%
Principal amount		$ 650,000,000
Total principal amount		650,000,000			650,000,000
4.125% notes, issued in September 2014 and due in October 2026
Debt
Principal amount		250,000,000
4.125% notes, issued in March 2017 and due in October 2026
Debt
Principal amount		$ 400,000,000
3.000% notes, issued in October 2016 and due in January 2027
Debt
Interest rate (as a percent)		3.00%	3.00%
Principal amount		$ 600,000,000
Total principal amount		$ 600,000,000			600,000,000
1.125% notes, issued in July 2021 and due in July 2027
Debt
Interest rate (as a percent)		1.125%	1.125%	1.125%
Principal amount | £			£ 400,000,000	£ 400,000,000
Total principal amount		$ 540,000,000			0
3.650% notes, issued in December 2017 and due in January 2028
Debt
Interest rate (as a percent)		3.65%	3.65%
Principal amount		$ 550,000,000
Total principal amount		$ 550,000,000			550,000,000
3.250% notes, issued in June 2019 and due in June 2029
Debt
Interest rate (as a percent)		3.25%	3.25%
Principal amount		$ 500,000,000
Total principal amount		$ 500,000,000			500,000,000
1.625% notes, issued in October 2020 and due in December 2030
Debt
Interest rate (as a percent)		1.625%	1.625%			1.625%
Principal amount | £			£ 400,000,000			£ 400,000,000
Total principal amount		$ 540,000,000			547,000,000
3.250% notes, $600 issued in May 2020 and $350 issued in July 2020, both due in January 2031
Debt
Interest rate (as a percent)		3.25%	3.25%
Principal amount		$ 950,000,000
Total principal amount		950,000,000			950,000,000
3.250% notes, issued in May 2020 and due in January 2031
Debt
Interest rate (as a percent)								3.25%
Principal amount		600,000,000						$ 600,000,000
3.250% notes, issued in July 2020 and due in January 2031
Debt
Interest rate (as a percent)							3.25%
Principal amount		$ 350,000,000					$ 350,000,000
1.800% notes, issued in December 2020 and due in March 2033
Debt
Interest rate (as a percent)		1.80%	1.80%
Principal amount		$ 400,000,000
Total principal amount		$ 400,000,000			400,000,000
1.750% notes, issued in July 2021 and due in July 2033
Debt
Interest rate (as a percent)		1.75%	1.75%	1.75%
Principal amount | £			£ 350,000,000	£ 350,000,000
Total principal amount		$ 473,000,000			0
2.730% notes, issued in May 2019 and due in May 2034
Debt
Interest rate (as a percent)		2.73%	2.73%
Principal amount | £			£ 315,000,000
Total principal amount		$ 425,000,000			431,000,000
5.875% bonds, $100 issued in March 2005 and $150 issued in June 2011, both due in March 2035
Debt
Interest rate (as a percent)		5.875%	5.875%
Principal amount		$ 250,000,000
Total principal amount		250,000,000			250,000,000
5.875% bonds, issued in March 2005 and due in March 2035
Debt
Principal amount		100,000,000
5.875% bonds, issued in June 2011 and due in March 2035
Debt
Principal amount		$ 150,000,000
4.650% notes, $300 issued in March 2017 and $250 issued in December 2017, both due in March 2047
Debt
Interest rate (as a percent)		4.65%	4.65%
Principal amount		$ 550,000,000
Total principal amount		550,000,000			$ 550,000,000
4.650% notes, issued in March 2017 and due in March 2047
Debt
Principal amount		300,000,000
4.650% notes, issued in December 2017 and due in March 2047
Debt
Principal amount		$ 250,000,000