Employee Bargaining Agreements and Benefit Plans - Plan's Assets Carried at Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	$ 15	$ 18
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	8	10
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	3	3
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	4	5
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	11	13
Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	8	10
Level 1 [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	3	3
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	4	5
Level 2 [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value Measurements	$ 4	$ 5