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Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2017
Cash and cash equivalents and restricted cash
Cash and cash equivalents			$ 42,023	$ 1,696
Total cash, cash equivalents and restricted cash in the statement of cash flows	$ 1,900	$ 3,520	42,264	1,900
Condensed Consolidated Statements of Cash Flows
Acquisitions (net of cash acquired) and other investments	(368)	(93)
Net cash used in investing activities	(131)	(537)
Net decrease in cash, cash equivalents and restricted cash	40,364	(1,137)
Cash, cash equivalents and restricted cash at the beginning of the period	1,900	3,520
Cash, cash equivalents and restricted cash at the end of the period	42,264	2,383
Adjustments Early Adoption \| ASU 2018-02 \| Adjustments
Condensed Consolidated Statements of Income
Amounts reclassified from accumulated other comprehensive income	(7)
ASU 2016-18
Cash and cash equivalents and restricted cash
Cash and cash equivalents			42,023	1,696
Total cash, cash equivalents and restricted cash in the statement of cash flows	1,900		42,264	1,900
Condensed Consolidated Statements of Cash Flows
Cash, cash equivalents and restricted cash at the beginning of the period	1,900
Cash, cash equivalents and restricted cash at the end of the period	$ 42,264
ASU 2016-18 \| Previously Reported
Cash and cash equivalents and restricted cash
Total cash, cash equivalents and restricted cash in the statement of cash flows		3,371
Condensed Consolidated Statements of Cash Flows
Acquisitions (net of cash acquired) and other investments		(110)
Net cash used in investing activities		(554)
Net decrease in cash, cash equivalents and restricted cash		(1,154)
Cash, cash equivalents and restricted cash at the beginning of the period		3,371
Cash, cash equivalents and restricted cash at the end of the period		2,217
ASU 2016-18 \| Adjustments
Cash and cash equivalents and restricted cash
Total cash, cash equivalents and restricted cash in the statement of cash flows		149
Condensed Consolidated Statements of Cash Flows
Acquisitions (net of cash acquired) and other investments		17
Net cash used in investing activities		17
Net decrease in cash, cash equivalents and restricted cash		17
Cash, cash equivalents and restricted cash at the beginning of the period		149
Cash, cash equivalents and restricted cash at the end of the period		$ 166
ASU 2016-18 \| Other Current Assets
Cash and cash equivalents and restricted cash
Restricted Cash and Cash Equivalents			14	14
ASU 2016-18 \| Other Long-Term Assets
Cash and cash equivalents and restricted cash
Restricted Cash and Cash Equivalents			$ 227	$ 190