Employee Retirement Benefits - Components of Net Periodic Costs for Qualified and Supplemental Pension Plans (Detail) - Qualified Pension Plans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure
Service cost	$ 2	$ 2
Interest cost	3	3
Expected return on plan assets	(5)	(5)
Amortization of actuarial loss and prior service cost	1	0
Other	0	1
Total non-service benefit	(1)	(1)
Net periodic benefit cost	$ 1	$ 1