Acquisitions and Divestitures - Narrative (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Acquisition [Line Items]
Intangible assets				$ 50,000,000
Revenue		$ 2,113,000,000	$ 2,048,000,000	4,579,000,000	$ 4,360,000,000
Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets				18,000,000
TRANZACT Acquisition [Member]
Business Acquisition [Line Items]
Business acquisition, effective date of acquisition	Jul. 30, 2019
Consideration paid in cash	$ 1,300,000,000
Business combination, contingent consideration arrangements, range of outcomes, value, high	17,000,000
Revenue		87,000,000		182,000,000
TRANZACT Acquisition [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible assets	$ 612,000,000
Intangible assets expected life	15 years 4 months 24 days
TRANZACT Acquisition [Member] | Term Loan [Member]
Business Acquisition [Line Items]
Debt instrument, term	1 year
TRANZACT Acquisition [Member] | Term Loan [Member] | Maximum [Member]
Business Acquisition [Line Items]
Debt instrument, face amount	$ 1,100,000,000
Other Acquisitions [Member]
Business Acquisition [Line Items]
Consideration paid in cash				72,000,000
Contingent consideration estimated fair value		$ 2,000,000		$ 2,000,000