Segment and Related Information - Goodwill (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill, Beginning Balance		$ 6,430	$ 6,247
Acquired goodwill		108	248
Divested goodwill			(25)
Impairments	$ (27)	(27)	(6)	$ (34)
Foreign currency translation		21	(34)
Goodwill, Ending Balance	6,532	6,532	6,430	6,247
Goodwill post-closing adjustment increase (decrease)		(3)
Tier 1 [Member]
Segment Reporting Information [Line Items]
Goodwill, Beginning Balance		2,193	2,117
Acquired goodwill		90	82
Divested goodwill			(6)
Goodwill, Ending Balance	2,283	2,283	2,193	2,117
Tier 2 [Member]
Segment Reporting Information [Line Items]
Goodwill, Beginning Balance		1,584	1,595
Acquired goodwill		12	23
Foreign currency translation		21	(34)
Goodwill, Ending Balance	1,617	1,617	1,584	1,595
Tier 3 [Member]
Segment Reporting Information [Line Items]
Goodwill, Beginning Balance		2,556	2,414
Acquired goodwill		6	142
Goodwill, Ending Balance	2,562	2,562	2,556	2,414
Other [Member]
Segment Reporting Information [Line Items]
Goodwill, Beginning Balance		97	121
Acquired goodwill			1
Divested goodwill			(19)
Impairments		(27)	(6)
Goodwill, Ending Balance	$ 70	$ 70	$ 97	$ 121

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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