Employee Benefits - Additional Information (Details) £ in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2020 GBP (£)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
U.K.
Defined Benefit Plan Disclosure [Line Items]
Non-cash settlement charge	$ 2	£ 2	$ 2	$ 0
Expected future employer cash contribution			5
Other
Defined Benefit Plan Disclosure [Line Items]
Non-cash settlement charge			0	0
Expected future employer cash contribution			19
U.S.
Defined Benefit Plan Disclosure [Line Items]
Non-cash settlement charge			0	$ 0
Expected future employer cash contribution			$ 99