Leases (Schedule of Maturity Analysis of Operating and Finance Lease Liabilities) (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019
Operating Lease Liabilities, Payments Due [Abstract]
Maturity of operating lease liabilities, 2019	$ 1
Maturity of operating lease liabilities, 2020	4
Maturity of operating lease liabilities, 2021	3
Maturity of operating lease liabilities, 2022	2
Maturity of operating lease liabilities, 2023	1
Maturity of operating lease liabilities, after 2023	23
Maturity of operating lease liabilities, total undiscounted lease payments	34
Operating lease liabilities, present value adjustment	(12)
Present value of operating lease liabilities	22	$ 19
Finance Lease Liabilities, Payments, Due [Abstract]
Maturity of finance lease liabilities, 2019	2
Maturity of finance lease liabilities, 2020	8
Maturity of finance lease liabilities, 2021	6
Maturity of finance lease liabilities, 2022	5
Maturity of finance lease liabilities, 2023	3
Maturity of finance lease liabilities, after 2023	6
Maturity of finance lease liabilities, total undiscounted lease payments	30
Finance lease liabilities, present value adjustment	(2)
Present value of finance lease liabilities	$ 28