Investments (Details) - Additional Information - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Proceeds from sales of real estate investments	$ 0	$ 74	$ 23
Gross gains on sales of real estate investments		23	10
Gross losses on sales of real estate investments		0	$ 0
Accumulated depreciation on real estate held for investment purposes	422	383
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2020	110
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2021	102
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2022	85
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2023	61
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2024	45
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2025 and thereafter	$ 71
Combined average days to maturity of short-term securities (in days)	54 days
Amortized cost of short-term securities (which approximates fair value)	$ 4,943	$ 3,985
Minimum percentage of equity interest that must be held by the Company in order for the investment in a VIE to be considered significant	20.00%

Combined average maturity (in days) on short-term securities.

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- Definition

The gross gain resulting from sales and other disposals of real estate owned for investment purposes.

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The gross loss resulting from sales and other disposals of real estate owned for investment purposes.

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- Definition

The minimum percentage of equity interest that must be held by the Company in order for the investment in a VIE to be considered significant.

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No definition available.

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Future rental payments receivable within one year of the balance sheet date under an operating lease.

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Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

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Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

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Future rental payments receivable within the third year from the balance sheet date under an operating lease.

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Future rental payments receivable within the second year from the balance sheet date under an operating lease.

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Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

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Amount of short-term investments classified as other.

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Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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The cumulative amount of depreciation for real estate property held for investment purposes.

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