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Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Cash and cash equivalents and restricted cash
Cash and cash equivalents				$ 43,815	$ 1,696
Total cash, cash equivalents and restricted cash in the statement of cash flows	$ 1,900	$ 1,900	$ 3,520	44,057	1,900
Condensed Consolidated Statements of Cash Flows
Acquisitions (net of cash acquired) and other investments		(573)	(275)
Net cash used in investing activities		(752)	(1,134)
Net decrease in cash, cash equivalents and restricted cash		42,157	(1,237)
Cash, cash equivalents and restricted cash at the beginning of the period	1,900	1,900	3,520
Cash, cash equivalents and restricted cash at the end of the period		44,057	2,283
Adjustments Early Adoption \| ASU 2018-02 \| Adjustments
Condensed Consolidated Statements of Operations
Amounts reclassified from accumulated other comprehensive income (loss)	(7)
ASU 2016-18
Cash and cash equivalents and restricted cash
Cash and cash equivalents				43,815	1,696
Total cash, cash equivalents and restricted cash in the statement of cash flows	1,900	1,900		44,057	1,900
Condensed Consolidated Statements of Cash Flows
Cash, cash equivalents and restricted cash at the beginning of the period	$ 1,900	1,900
Cash, cash equivalents and restricted cash at the end of the period		$ 44,057
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			(315)
Net cash used in investing activities			(1,174)
Net decrease in cash, cash equivalents and restricted cash			(1,277)
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			2,094
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			40
Net cash used in investing activities			40
Net decrease in cash, cash equivalents and restricted cash			40
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			$ 189
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				$ 228	$ 190