Condensed Consolidating Financial Statements (Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Consolidating Financial Information [Line Items]
Net cash provided by operating activities	[1]	$ 2,981	$ 3,148	$ 3,876
Cash flows from investing activities:
Business acquisitions, net of cash acquired		(19)	(10,099)	(399)
Capital expenditures		(987)	(690)	(428)
Proceeds from sales of assets		14	562	50
Other, net		(7)	(7)	39
Net cash used by investing activities		(994)	(10,234)	(788)
Cash flows from financing activities:
Proceeds from notes		0	6,461	985
Purchases of common stock		(231)	(1,769)	(1,558)
Dividends paid		(1,152)	(1,075)	(986)
Repayment of fixed-rate notes		0	0	(900)
(Repayments of) proceeds from commercial paper, net		(850)	850	0
Repayment of CSRA accounts receivable purchase agreement		0	(450)	0
Amortization of intangible and finance lease right-of-use assets		363	327	79
Other, net		236	69	60
Net cash (used) provided by financing activities		(1,997)	5,086	(2,399)
Net cash used by discontinued operations		(51)	(20)	(40)
Cash sweep/funding by parent		0	0	0
Net (decrease) increase in cash and equivalents		(61)	(2,020)	649
Cash and equivalents at beginning of year		963	2,983	2,334
Cash and equivalents at end of year		902	963	2,983
LIBOR
Cash flows from financing activities:
Proceeds from notes		0	1,000	0
Consolidating Adjustments
Condensed Consolidating Financial Information [Line Items]
Net cash provided by operating activities	[1]	0	0	0
Cash flows from investing activities:
Business acquisitions, net of cash acquired			0	0
Capital expenditures		0	0	0
Proceeds from sales of assets			0
Other, net		0	0	0
Net cash used by investing activities		0	0	0
Cash flows from financing activities:
Proceeds from notes			0	0
Purchases of common stock		0	0	0
Dividends paid		0	0	0
Repayment of fixed-rate notes				0
(Repayments of) proceeds from commercial paper, net		0	0
Repayment of CSRA accounts receivable purchase agreement			0
Other, net		0	0	0
Net cash (used) provided by financing activities		0	0	0
Net cash used by discontinued operations		0	0	0
Cash sweep/funding by parent		0	0	0
Net (decrease) increase in cash and equivalents		0	0	0
Cash and equivalents at beginning of year		0	0	0
Cash and equivalents at end of year		0	0	0
Consolidating Adjustments | LIBOR
Cash flows from financing activities:
Proceeds from notes			0
Parent
Condensed Consolidating Financial Information [Line Items]
Net cash provided by operating activities	[1]	(46)	(579)	312
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(9,749)	0
Capital expenditures		(68)	(51)	(26)
Proceeds from sales of assets			90
Other, net		7	4	10
Net cash used by investing activities		(61)	(9,706)	(16)
Cash flows from financing activities:
Proceeds from notes			6,461	985
Purchases of common stock		(231)	(1,769)	(1,558)
Dividends paid		(1,152)	(1,075)	(986)
Repayment of fixed-rate notes				(900)
(Repayments of) proceeds from commercial paper, net		(850)	850
Repayment of CSRA accounts receivable purchase agreement			0
Other, net		24	3	63
Net cash (used) provided by financing activities		(2,209)	5,470	(2,396)
Net cash used by discontinued operations		(51)	(20)	(40)
Cash sweep/funding by parent		2,508	3,365	2,816
Net (decrease) increase in cash and equivalents		141	(1,470)	676
Cash and equivalents at beginning of year		460	1,930	1,254
Cash and equivalents at end of year		601	460	1,930
Parent | LIBOR
Cash flows from financing activities:
Proceeds from notes			1,000
Guarantors on a Combined Basis
Condensed Consolidating Financial Information [Line Items]
Net cash provided by operating activities	[1]	2,918	2,954	2,371
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(74)	(350)
Capital expenditures		(718)	(513)	(330)
Proceeds from sales of assets			472
Other, net		10	(12)	31
Net cash used by investing activities		(708)	(127)	(649)
Cash flows from financing activities:
Proceeds from notes			0	0
Purchases of common stock		0	0	0
Dividends paid		0	0	0
Repayment of fixed-rate notes				0
(Repayments of) proceeds from commercial paper, net		0	0
Repayment of CSRA accounts receivable purchase agreement			0
Other, net		(2)	35	(3)
Net cash (used) provided by financing activities		(2)	35	(3)
Net cash used by discontinued operations		0	0	0
Cash sweep/funding by parent		(2,208)	(2,862)	(1,719)
Net (decrease) increase in cash and equivalents		0	0	0
Cash and equivalents at beginning of year		0	0	0
Cash and equivalents at end of year		0	0	0
Guarantors on a Combined Basis | LIBOR
Cash flows from financing activities:
Proceeds from notes			0
Other Subsidiaries on a Combined Basis
Condensed Consolidating Financial Information [Line Items]
Net cash provided by operating activities	[1]	109	773	1,193
Cash flows from investing activities:
Business acquisitions, net of cash acquired			(276)	(49)
Capital expenditures		(201)	(126)	(72)
Proceeds from sales of assets			0
Other, net		(24)	1	(2)
Net cash used by investing activities		(225)	(401)	(123)
Cash flows from financing activities:
Proceeds from notes			0	0
Purchases of common stock		0	0	0
Dividends paid		0	0	0
Repayment of fixed-rate notes				0
(Repayments of) proceeds from commercial paper, net		0	0
Repayment of CSRA accounts receivable purchase agreement			(450)
Other, net		214	31	0
Net cash (used) provided by financing activities		214	(419)	0
Net cash used by discontinued operations		0	0	0
Cash sweep/funding by parent		(300)	(503)	(1,097)
Net (decrease) increase in cash and equivalents		(202)	(550)	(27)
Cash and equivalents at beginning of year		503	1,053	1,080
Cash and equivalents at end of year		$ 301	503	$ 1,053
Other Subsidiaries on a Combined Basis | LIBOR
Cash flows from financing activities:
Proceeds from notes			$ 0

[1] * Continuing operations only.