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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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Fair Value Measurements, Other Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Financial assets:
Cash and cash equivalents, at carrying amount	$ 3,551	$ 5,850	$ 5,176	$ 4,816
Financial liabilities:
Debt (excluding capital leases), at carrying amount	8,467	8,310
Fair Value, Inputs, Level 1 [Member]
Financial assets:
Cash and cash equivalents, at fair value	3,551	5,850
Fair Value, Inputs, Level 2 [Member]
Financial liabilities:
Debt (excluding capital leases), at fair value	$ 9,328	$ 9,795