v3.8.0.1

Fair Value Measurements - Fair Value Measurements By Level for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 4,072	$ 3,930
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	195	236
Corporate securities	2,210	1,932
Municipal securities	2,087	1,733
Asset-backed securities	437	317
Total investments	5,532	4,771
Restricted deposits available for sale:
Cash and cash equivalents	17	6
Certificates of deposit	4	5
U.S. Treasury securities and obligations of U.S. government corporations and agencies	114	127
Total restricted deposits	135	138
Other long-term assets:
Interest rate swap agreements	1	4
Total assets at fair value	9,740	8,843
Liabilities
Interest rate swap agreements	72	62
Total liabilities at fair value	72	62
Residential mortgage-backed securities
Investments available for sale:
Mortgage-backed securities	332	215
Commercial mortgage- backed securities
Investments available for sale:
Mortgage-backed securities	271	338
Level I
Assets
Cash and cash equivalents	4,072	3,930
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	195	221
Corporate securities	0	0
Municipal securities	0	0
Asset-backed securities	0	0
Total investments	195	221
Restricted deposits available for sale:
Cash and cash equivalents	17	6
Certificates of deposit	4	5
U.S. Treasury securities and obligations of U.S. government corporations and agencies	114	127
Total restricted deposits	135	138
Other long-term assets:
Interest rate swap agreements	0	0
Total assets at fair value	4,402	4,289
Liabilities
Interest rate swap agreements	0	0
Total liabilities at fair value	0	0
Level I | Residential mortgage-backed securities
Investments available for sale:
Mortgage-backed securities	0	0
Level I | Commercial mortgage- backed securities
Investments available for sale:
Mortgage-backed securities	0	0
Level II
Assets
Cash and cash equivalents	0	0
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	0	15
Corporate securities	2,210	1,932
Municipal securities	2,087	1,733
Asset-backed securities	437	317
Total investments	5,337	4,550
Restricted deposits available for sale:
Cash and cash equivalents	0	0
Certificates of deposit	0	0
U.S. Treasury securities and obligations of U.S. government corporations and agencies	0	0
Total restricted deposits	0	0
Other long-term assets:
Interest rate swap agreements	1	4
Total assets at fair value	5,338	4,554
Liabilities
Interest rate swap agreements	72	62
Total liabilities at fair value	72	62
Level II | Residential mortgage-backed securities
Investments available for sale:
Mortgage-backed securities	332	215
Level II | Commercial mortgage- backed securities
Investments available for sale:
Mortgage-backed securities	271	338
Level III
Assets
Cash and cash equivalents	0	0
Investments available for sale:
U.S. Treasury securities and obligations of U.S. government corporations and agencies	0	0
Corporate securities	0	0
Municipal securities	0	0
Asset-backed securities	0	0
Total investments	0	0
Restricted deposits available for sale:
Cash and cash equivalents	0	0
Certificates of deposit	0	0
U.S. Treasury securities and obligations of U.S. government corporations and agencies	0	0
Total restricted deposits	0	0
Other long-term assets:
Interest rate swap agreements	0	0
Total assets at fair value	0	0
Liabilities
Interest rate swap agreements	0	0
Total liabilities at fair value	0	0
Level III | Residential mortgage-backed securities
Investments available for sale:
Mortgage-backed securities	0	0
Level III | Commercial mortgage- backed securities
Investments available for sale:
Mortgage-backed securities	$ 0	$ 0

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- Definition

This element represents asset backed securities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

+ References

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- Definition

This element represents restricted cash and cash equivalents reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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- Definition

This element represents restricted certificates of deposit reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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Corporate securities

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- Definition

This element represents total restricted deposits reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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This element represents U.S. Treasury securities and obligations of U.S. government corporations and agencies reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

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