Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Merger and integration expense	$ 46	$ 101	$ 147	$ 121
Personal expense
Business Acquisition [Line Items]
Merger and integration expense	10	35	47	41
Legal and professional fees
Business Acquisition [Line Items]
Merger and integration expense	9	31	15	38
Contribution expense
Business Acquisition [Line Items]
Merger and integration expense	0	20	0	20
Other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 27	$ 15	$ 85	$ 22