Acquisitions and Dispositions of Businesses - Completed Dispositions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) numberOfDisposition	Dec. 31, 2019 USD ($) numberOfDisposition	Dec. 31, 2018 USD ($) numberOfDisposition
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gains (losses) on disposal of businesses	$ 25	$ 13	$ (6)
Disposal Group, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of dispositions | numberOfDisposition	1	8	4
Amortization and Impairment of Intangible Assets | Disposal Group, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-cash impairment charge of disposition			$ 176