Acquisitions and Dispositions of Businesses - Dispositions (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($) disposal	Sep. 30, 2019 USD ($) disposal	Sep. 30, 2020 USD ($) disposal	Sep. 30, 2019 USD ($) disposal
Dispositions
Pretax gains (losses) recognized on disposal of businesses \| $	$ 0	$ 1	$ 25	$ 8
Disposal Group, Not Discontinued Operations
Dispositions
Number of dispositions \| disposal	0	2	1	6

Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration