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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair Value Measurements, Other Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Financial assets:
Cash and cash equivalents, at carrying amount	$ 4,451	$ 5,850	$ 5,207	$ 4,816
Financial liabilities:
Debt (excluding capital leases), at carrying amount	8,451	8,310
Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents, at fair value	4,451	5,850
Fair Value, Inputs, Level 2 [Member]
Financial liabilities:
Debt (excluding capital leases), at fair value	$ 9,310	$ 9,795