Revenue Recognition - Impacts of ASC 606 on Consolidated Statement of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	May 11, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income		$ 227	$ 232	$ 901	$ 700
Adjustments to reconcile net income to net cash provided by operating activities from continuing operations:
Depreciation and other amortization				286	213
Amortization of acquisition-related intangible assets				120	117
Share-based compensation				54	48
Deferred income taxes				105	20
(Gain) loss on sale of businesses		2	0	(227)	(10)
Loss on early debt extinguishment		8	0	8	0
Income from investments in unconsolidated affiliates		(1)	(5)	(8)	(31)
Dividends from unconsolidated affiliates				1	44
Non-cash impairment charges				3	17
Changes in assets and liabilities, net of effects from acquisitions and dispositions:
Trade accounts receivable				(29)	23
Prepaid expenses and other assets				(63)	(48)
Contract costs				(107)	(20)
Accounts payable and other liabilities				48	(9)
Contract liabilities				(111)	(45)
Net cash provided by operating activities from continuing operations				981	1,015
Cash flows from investing activities:
Capital expenditures, including capitalization of software costs				(263)	(208)
Proceeds from sale of businesses	$ 19			419	19
Other investing activities				(13)	7
Net cash provided by (used in) investing activities from continuing operations				143	(575)
Cash flows from financing activities:
Debt proceeds				3,627	1,946
Debt repayments, including redemption and other costs				(3,256)	(1,410)
Proceeds from issuance of treasury stock				60	65
Purchases of treasury stock, including employee shares withheld for tax obligations				(1,254)	(1,016)
Other financing activities				4	0
Net cash used in financing activities from continuing operations				(819)	(415)
Net change in cash and cash equivalents from continuing operations				305	25
Net change in cash and cash equivalents from discontinued operations				43	0
Cash and cash equivalents, beginning balance				325	300
Cash and cash equivalents, ending balance		673	$ 325	673	325
Discontinued operations cash flow information:
Net cash used in operating activities				(7)	0
Net cash provided by investing activities				50	0
Net change in cash and cash equivalents from discontinued operations				43	$ 0
Adjustments | Accounting Standards Update 2014-09
Cash flows from operating activities:
Net income		(10)		(49)
Adjustments to reconcile net income to net cash provided by operating activities from continuing operations:
Depreciation and other amortization				(54)
Amortization of acquisition-related intangible assets				0
Share-based compensation				0
Deferred income taxes				(14)
(Gain) loss on sale of businesses		0		(3)
Loss on early debt extinguishment		0		0
Income from investments in unconsolidated affiliates		0		0
Dividends from unconsolidated affiliates				0
Non-cash impairment charges				0
Changes in assets and liabilities, net of effects from acquisitions and dispositions:
Trade accounts receivable				41
Prepaid expenses and other assets				(1)
Contract costs				67
Accounts payable and other liabilities				(4)
Contract liabilities				17
Net cash provided by operating activities from continuing operations				0
Cash flows from investing activities:
Capital expenditures, including capitalization of software costs				0
Proceeds from sale of businesses				0
Other investing activities				0
Net cash provided by (used in) investing activities from continuing operations				0
Cash flows from financing activities:
Debt proceeds				0
Debt repayments, including redemption and other costs				0
Proceeds from issuance of treasury stock				0
Purchases of treasury stock, including employee shares withheld for tax obligations				0
Other financing activities				0
Net cash used in financing activities from continuing operations				0
Net change in cash and cash equivalents from continuing operations				0
Net change in cash and cash equivalents from discontinued operations				0
Cash and cash equivalents, beginning balance				0
Cash and cash equivalents, ending balance		0		0
Discontinued operations cash flow information:
Net cash used in operating activities				0
Net cash provided by investing activities				0
Net change in cash and cash equivalents from discontinued operations				0
Balances without adoption of ASC 606
Cash flows from operating activities:
Net income		217		852
Adjustments to reconcile net income to net cash provided by operating activities from continuing operations:
Depreciation and other amortization				232
Amortization of acquisition-related intangible assets				120
Share-based compensation				54
Deferred income taxes				91
(Gain) loss on sale of businesses		2		(230)
Loss on early debt extinguishment		8		8
Income from investments in unconsolidated affiliates		(1)		(8)
Dividends from unconsolidated affiliates				1
Non-cash impairment charges				3
Changes in assets and liabilities, net of effects from acquisitions and dispositions:
Trade accounts receivable				12
Prepaid expenses and other assets				(64)
Contract costs				(40)
Accounts payable and other liabilities				44
Contract liabilities				(94)
Net cash provided by operating activities from continuing operations				981
Cash flows from investing activities:
Capital expenditures, including capitalization of software costs				(263)
Proceeds from sale of businesses				419
Other investing activities				(13)
Net cash provided by (used in) investing activities from continuing operations				143
Cash flows from financing activities:
Debt proceeds				3,627
Debt repayments, including redemption and other costs				(3,256)
Proceeds from issuance of treasury stock				60
Purchases of treasury stock, including employee shares withheld for tax obligations				(1,254)
Other financing activities				4
Net cash used in financing activities from continuing operations				(819)
Net change in cash and cash equivalents from continuing operations				305
Net change in cash and cash equivalents from discontinued operations				43
Cash and cash equivalents, beginning balance				325
Cash and cash equivalents, ending balance		$ 673		673
Discontinued operations cash flow information:
Net cash used in operating activities				(7)
Net cash provided by investing activities				50
Net change in cash and cash equivalents from discontinued operations				$ 43