Schedule I Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Cash flows from operating activities	$ 13,596	$ 9,795	$ 9,740
Investing activities
Cash paid for acquisitions	(2,131)	(1,760)	(16,164)
Other, net	126	(37)	144
Cash flows from (used for) investing activities	(8,599)	(9,355)	(18,395)
Financing activities
Common stock repurchases	(1,500)	(1,280)	(1,200)
Proceeds from common stock issuances	688	429	402
(Repayments of) proceeds from commercial paper, net	(3,508)	(382)	3,666
Proceeds from issuance of long-term debt	5,291	3,968	11,982
Repayments of long-term debt	(4,398)	(2,596)	(1,041)
Other, net	(413)	(581)	(552)
Cash flows (used for) from financing activities	(3,441)	(1,011)	12,239
Increase (decrease) in cash and cash equivalents	1,551	(493)	3,428
Cash and cash equivalents, beginning of period	10,430	10,923	7,495
Cash and cash equivalents, end of period	11,981	10,430	10,923
Supplemental cash flow disclosures
Cash paid for interest	1,133	1,055	639
Cash paid for income taxes	4,004	4,726	4,401
Supplemental schedule of non-cash investing activities
Common stock issued for acquisitions	2,164	0	0
Parent Company [Member]
Operating activities
Cash flows from operating activities	2,021	4,294	1,727
Investing activities
Repayments (issuances) of notes to subsidiaries	(2,071)	824	5,064
Cash paid for acquisitions	(2,313)	(2,292)	(12,270)
Return of capital to parent company	3,375	2,143	4,375
Capital contributions to subsidiaries	(959)	(765)	(1,109)
Other, net	0	168	140
Cash flows from (used for) investing activities	2,174	(1,570)	(13,928)
Financing activities
Common stock repurchases	(1,500)	(1,280)	(1,200)
Proceeds from common stock issuances	688	429	402
Cash dividends paid	(2,773)	(2,261)	(1,786)
(Repayments of) proceeds from commercial paper, net	(3,508)	(382)	3,666
Proceeds from issuance of long-term debt	5,291	3,968	11,982
Repayments of long-term debt	(3,472)	(2,596)	(1,041)
Proceeds from (Repayments of) Related Party Debt	1,704	(30)	95
Other, net	(446)	(421)	(447)
Cash flows (used for) from financing activities	(4,016)	(2,573)	11,671
Increase (decrease) in cash and cash equivalents	179	151	(530)
Cash and cash equivalents, beginning of period	180	29	559
Cash and cash equivalents, end of period	359	180	29
Supplemental cash flow disclosures
Cash paid for interest	1,062	974	573
Cash paid for income taxes	3,455	4,557	4,294
Supplemental schedule of non-cash investing activities
Common stock issued for acquisitions	2,164	0	0
Conversion of note receivable from subsidiaries to equity	$ 4,378	$ 0	$ 0