Employee Benefits - Summary of Employer Contributions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 12	$ 49	$ 74	$ 102
U.K.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	2	2	8	6
Other
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	2	3	12	14
U.S.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 8	$ 44	$ 54	$ 82