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Summary of Significant Accounting Policies - Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies
Current restricted trust and escrow accounts	$ 75	$ 70
Equity method investments	314	377
Investments without readily determinable fair values	63	57
Redeemable preferred stock	49	49
Investments in unconsolidated entities	$ 426	$ 483

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Amount of investment in equity security without readily determinable fair value.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117539-209714

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Amount of investment in equity method investee and investment in and advance to affiliate.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
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The current cash, cash equivalents and investments that are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. Includes current cash equivalents and investments that are similarly restricted as to withdrawal, usage or disposal.

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Amount of investment in redeemable preferred stock measured at fair value with change in fair value recognized in net income (FV-NI).

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