Senior Notes and Other Debt (Summary of Senior Notes Payable and Other Debt) (Details) $ in Thousands, $ in Millions	Dec. 31, 2019 USD ($)	Nov. 30, 2019 CAD ($)	Sep. 30, 2019 CAD ($)	Aug. 31, 2019 USD ($)	Jul. 01, 2019 USD ($)	Jun. 30, 2019 USD ($)	Feb. 28, 2019 USD ($)	Jan. 03, 2019	Dec. 31, 2018 USD ($)	Aug. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)
Debt Instrument [Line Items]
Commercial paper	$ 567,450								$ 0
Long-term debt, gross	12,245,802
Long-term debt and short-term borrowings, gross	12,245,802								10,829,702
Debt issuance costs, net	(79,939)								(69,615)
Debt instrument, unamortized discount	(27,146)								(25,225)
Debt, Long-term and Short-term, Combined Amount	12,158,773								10,733,699
Unamortized fair value adjustment	$ 20,056								(1,163)
3.00% Senior Notes, Series A due 2019
Debt Instrument [Line Items]
Interest rate	3.00%		3.00%
Senior notes	$ 0								293,319
2.70% Senior Notes due 2020
Debt Instrument [Line Items]
Interest rate	2.70%			2.70%	2.70%
Senior notes	$ 0								500,000
Floating Rate, Series F due 2021
Debt Instrument [Line Items]
Senior notes	$ 231,018								0
4.25% Senior Notes due 2022
Debt Instrument [Line Items]
Interest rate	4.25%		4.25%	4.25%
Senior notes	$ 0								600,000
3.25% Senior Notes due 2022
Debt Instrument [Line Items]
Interest rate	3.25%
Senior notes									500,000
3.30% Senior Notes, Series C due 2022
Debt Instrument [Line Items]
Interest rate	3.30%
Senior notes	$ 192,515								183,325
Unsecured Term Loan Due 2023
Debt Instrument [Line Items]
Unsecured debt	$ 200,000					$ 300,000			300,000
3.125% Senior Notes due 2023
Debt Instrument [Line Items]
Interest rate	3.125%
Senior notes	$ 400,000								400,000
3.10% Senior Notes due 2023
Debt Instrument [Line Items]
Interest rate	3.10%
Senior notes	$ 400,000								400,000
2.55% Senior Notes, Series D due 2023
Debt Instrument [Line Items]
Interest rate	2.55%
Senior notes	$ 211,767								201,657
Unsecured Term Loan Due 2024
Debt Instrument [Line Items]
Unsecured debt	$ 0								600,000
3.50% Senior Notes due 2024
Debt Instrument [Line Items]
Interest rate	3.50%						3.50%
Senior notes	$ 400,000						$ 400,000		0
3.75% Senior Notes due 2024
Debt Instrument [Line Items]
Interest rate	3.75%
Senior notes	$ 400,000								400,000
4.125% Senior Notes, Series B due 2024
Debt Instrument [Line Items]
Interest rate	4.125%
Senior notes	$ 192,515								183,324
2.80% Senior Notes, Series E due 2024
Debt Instrument [Line Items]
Interest rate	2.80%	2.80%
Senior notes	$ 462,036	$ 600							0
Unsecured Term Loan due 2025
Debt Instrument [Line Items]
Unsecured debt	$ 385,030		$ 500						0
3.50% Senior Notes due 2025
Debt Instrument [Line Items]
Interest rate	3.50%
Senior notes	$ 600,000								600,000
2.65% Senior Notes due 2025
Debt Instrument [Line Items]
Interest rate	2.65%				2.65%
Senior notes	$ 450,000				$ 450,000				0
4.125% Senior Notes due 2026
Debt Instrument [Line Items]
Interest rate	4.125%
Senior notes	$ 500,000								500,000
3.25% Senior Notes due 2026
Debt Instrument [Line Items]
Interest rate	3.25%
Senior notes	$ 450,000								450,000
3.85% Senior Notes due 2027
Debt Instrument [Line Items]
Interest rate	3.85%
Senior notes	$ 400,000								400,000
4.00% Senior Notes due 2028
Debt Instrument [Line Items]
Interest rate	4.00%										4.00%
Senior notes	$ 650,000								650,000		$ 650,000
4.40% Senior Notes due 2029
Debt Instrument [Line Items]
Interest rate	4.40%									4.40%
Senior notes	$ 750,000								750,000	$ 750,000
3.00% Senior Notes due 2030
Debt Instrument [Line Items]
Interest rate	3.00%			3.00%
Senior notes	$ 650,000			$ 650,000					0
6.90% Senior Notes due 2037
Debt Instrument [Line Items]
Interest rate	6.90%
Senior notes	$ 52,400								52,400
6.59% Senior Notes due 2038
Debt Instrument [Line Items]
Interest rate	6.59%
Senior notes	$ 22,823								22,823
5.45% Senior Notes due 2043
Debt Instrument [Line Items]
Interest rate	5.45%							5.45%
Senior notes	$ 0								258,750
5.70% Senior Notes due 2043
Debt Instrument [Line Items]
Interest rate	5.70%
Senior notes	$ 300,000								300,000
4.375% Senior Notes due 2045
Debt Instrument [Line Items]
Interest rate	4.375%
Senior notes	$ 300,000								300,000
4.875% Senior Notes due 2049
Debt Instrument [Line Items]
Interest rate	4.875%						4.875%
Senior notes	$ 300,000						$ 300,000		0
Mortgage loans and other
Debt Instrument [Line Items]
Long-term debt, gross	1,996,969								1,127,697
Revolving Credit Facility | Unsecured revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	120,787								765,919
Revolving Credit Facility | Unsecured revolving credit facility | Borrowings originally denominated in CAD
Debt Instrument [Line Items]
Long-term debt, gross	26,200								23,100
Revolving Credit Facility | Unsecured revolving credit facility | Borrowings originally denominated in GBP
Debt Instrument [Line Items]
Long-term debt, gross	27,600								27,800
Revolving Credit Facility | Secured revolving construction credit facility due 2022
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$ 160,492								$ 90,488