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Financial Instruments and Derivatives - Additional Information (Details)	9 Months Ended
	Sep. 30, 2019 USD ($) Contract $ / shares	Dec. 31, 2018 USD ($)
Derivative
Preferred Stock, Redemption Price Per Share | $ / shares	$ 50
Preferred Stock, Redemption Date	Oct. 01, 2026
net liability position [Member]
Derivative
Credit Risk Related Contingent Features Termination Value	$ 10,200,000
Fair Value, Measurements, Recurring [Member]
Derivative
Interest Rate Derivative Assets, at Fair Value	500,000	$ 3,700,000
Interest Rate Derivative Liabilities, at Fair Value	10,500,000	5,300,000
Embedded Derivative, Fair Value of Embedded Derivative Asset	38,200,000	18,600,000
Forward Swaps on future expected debt issuance [Member]
Derivative
Cash Flow Hedges Derivative Instruments at Fair Value, Net	$ 150,000,000.0
Maximum Length of Time Hedged in Cash Flow Hedge	10 years
Designated as Hedging Instrument | Interest Expense
Derivative
Change in fair value of interest rate derivatives included in AOCI and expected to be reclassified in the next 12 months	$ 1,000,000.0
Designated as Hedging Instrument | Interest Rate Swap [Member]
Derivative
Derivative, Number of Instruments Held | Contract	4
Derivative, Notional Amount	$ 300,000,000.0
Conventional Variable Rate Debt [Member] | Minimum [Member]
Derivative
Debt Renewal Period	30 days
Conventional Variable Rate Debt [Member] | Maximum [Member]
Derivative
Debt Renewal Period	90 days
Fixed Rate Debt [Member]
Derivative
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	$ 3,800,000,000	3,100,000,000
Notes Payable, Fair Value Disclosure	4,100,000,000	3,100,000,000
Floating Rate Debt [Member]
Derivative
Notes Payable Excluding Interest Rate Swaps and Cap Agreements	500,000,000	1,100,000,000
Notes Payable, Fair Value Disclosure	$ 500,000,000	$ 1,100,000,000

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