Employee Benefits - Summary of Employer Contributions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 49	$ 29	$ 102	$ 108
U.K.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	2	19	6	65
Other
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	3	3	14	13
U.S.
Defined Benefit Plan Disclosure [Line Items]
Company’s benefit pension plans	$ 44	$ 7	$ 82	$ 30