Additional Financial Information (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 6,588	$ 8,657	$ 5,204	$ 50,498
Restricted cash in Other current assets	15	56	61	6
Restricted cash in Other Assets	179	75	135	428
Cash and cash equivalents and restricted cash	6,782	8,788	$ 5,400	$ 50,932
Cash Paid for Amounts Included in the Measurement of Lease Liabilities [Abstract]
Operating cash flows from operating leases	3,338	3,694
Operating lease right-of-use assets obtained in exchange for new operating lease obligations	7,068	0
Cash paid (refunded) during the year for:
Interest	6,938	6,943
Income taxes, net of refunds	$ 420	$ (537)

Amount 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.

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Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, 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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