Accounting Policies - New Accounting Pronouncements (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)
New Accounting Pronouncements or Change in Accounting Principle
Income tax provision	$ 777	$ 921	$ 2,115	$ 2,271
Condensed Consolidated Statements of Cash Flows
Cash paid to other suppliers and employees			(11,230)	(11,020)
Net cash provided by operating activities			8,143	8,020
Net cash used in financing activities			(7,421)	(6,640)
Reconciliation of net income to net cash provided by operating activities:
Accrued expenses			1,670	2,149
Condensed Consolidated Statements of Income
Operating expenses	4,627	4,668	14,232	13,885
Operating profit	2,499	2,824	6,409	7,366
Other expense	192	7	206	23
Previously Reported
Condensed Consolidated Statements of Cash Flows
Cash paid to other suppliers and employees				(11,092)
Net cash provided by operating activities				7,948
Excess tax benefits from stock-based compensation				72
Net cash used in financing activities				(6,568)
Reconciliation of net income to net cash provided by operating activities:
Accrued expenses				2,077
Condensed Consolidated Statements of Income
Operating expenses		4,675		13,908
Operating profit		2,817		7,343
Adjustment
Condensed Consolidated Statements of Cash Flows
Cash paid to other suppliers and employees				72
Net cash provided by operating activities				72
Excess tax benefits from stock-based compensation				(72)
Net cash used in financing activities				(72)
Reconciliation of net income to net cash provided by operating activities:
Accrued expenses				72
Condensed Consolidated Statements of Income
Operating expenses		(7)		(23)
Operating profit		7		23
Other expense		$ 7		$ 23
ASU 2016-09 | Previously Reported
New Accounting Pronouncements or Change in Accounting Principle
Income tax provision	$ (18)		$ (51)
ASU 2014-09 | Retail/LTC Segment
Condensed Consolidated Statements of Income
Number of differences related to revenue accounting for ExtraBucks Rewards customer loyalty program | item			1