Employee Retirement Benefits - Components of Net Periodic Costs for Qualified and Supplemental Pension Plans (Detail) - Qualified Pension Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure
Service cost	$ 2	$ 3	$ 6	$ 8
Interest cost	4	4	10	10
Expected return on plan assets	(5)	(6)	(15)	(17)
Amortization of actuarial loss and prior service cost	0	0	1	1
Other	0	0	1	0
Total non-service benefit	(1)	(2)	(3)	(6)
Net periodic benefit cost	$ 1	$ 1	$ 3	$ 2