v3.26.1
Segment Information - Revenue (Net of Reimbursable Expenses) of the Reported Segments (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting Information [Line Items]        
Total revenue $ 2,466 $ 2,261 $ 4,878 $ 4,484
Depreciation     111 111
Income from operations 364 368 812 800
HWC [Member]        
Segment Reporting Information [Line Items]        
Total revenue 1,292 1,198 2,576 2,380
R&B [Member]        
Segment Reporting Information [Line Items]        
Total revenue 1,168 1,050 2,287 2,080
Operating Segments [Member]        
Segment Reporting Information [Line Items]        
Segment revenue excluding interest income 2,403 2,197 4,751 4,360
Interest income 31 30 64 59
Total revenue 2,434 2,227 4,815 4,419
Other segment expense 1,829 1,683 3,570 3,297
Depreciation 41 42 83 83
Total segment expense 1,870 1,725 3,653 3,380
Income from operations 564 502 1,162 1,039
Operating Segments [Member] | HWC [Member]        
Segment Reporting Information [Line Items]        
Segment revenue excluding interest income 1,263 1,173 2,520 2,331
Interest income 7 7 15 14
Total revenue 1,270 1,180 2,535 2,345
Other segment expense 933 868 1,820 1,691
Depreciation 31 32 63 63
Total segment expense 964 900 1,883 1,754
Income from operations 306 280 652 591
Operating Segments [Member] | R&B [Member]        
Segment Reporting Information [Line Items]        
Segment revenue excluding interest income 1,140 1,024 2,231 2,029
Interest income 24 23 49 45
Total revenue 1,164 1,047 2,280 2,074
Other segment expense 896 815 1,750 1,606
Depreciation 10 10 20 20
Total segment expense 906 825 1,770 1,626
Income from operations $ 258 $ 222 $ 510 $ 448