Segment Information - Revenue (Net of Reimbursable Expenses) of the Reported Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 2,031	$ 2,091	$ 4,191	$ 4,319
Income from operations	137	170	316	381
HWC [Member]
Segment Reporting Information [Line Items]
Revenues	1,173	1,193	2,430	2,439
R&B [Member]
Segment Reporting Information [Line Items]
Revenues	854	887	1,748	1,812
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	2,011	2,064	4,146	4,221
Income from operations	385	422	834	867
Operating Segments [Member] | HWC [Member]
Segment Reporting Information [Line Items]
Revenues	1,159	1,179	2,403	2,412
Income from operations	217	218	474	460
Operating Segments [Member] | R&B [Member]
Segment Reporting Information [Line Items]
Revenues	852	885	1,743	1,809
Income from operations	$ 168	$ 204	$ 360	$ 407