Pension Plans, Postretirement and Other Employee Benefits - Additional Information (Detail) $ in Millions		1 Months Ended	3 Months Ended			12 Months Ended
	Jan. 02, 2012 retirement_plan	Feb. 29, 2016 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2015	Dec. 31, 2014 USD ($) retiree	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Pension and Other Postretirement Benefits Disclosure [Line Items]
Pension benefit obligations						$ 710
Pension benefit obligations with funding requirements						641
Pension Fund assets available to fund pension benefit obligations						561
Pension benefit obligations with no funding requirements						$ 69
Acceptable tolerance limit of investment allocations for securities						5.00%
Employer contributions		$ 18				$ 37
Expected contributions in 2013						32
Non-cash contribution charge		$ 72				$ 21
Minimum retirement age for eligible employees of the post retirement plans						55 years
Minimum years of service for eligible employees of the post retirement plans						10 years
Prior period correction					$ 11
Defined Benefit Plan, Prior Period Adjustment, Number of Retirees Entitled to Benefits Not Included | retiree					170
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate						7.00%	7.00%	6.50%
Defined Benefit Plan Ultimate Health Care Cost Year Five						4.50%	4.50%	4.50%
Retirement Savings Plan | retirement_plan	1
Maximum percentage of salary deferral allowed under the Employee Stock Ownership Plans						75.00%
Defined Compensation Plan, Amended Employee Match Percentage on One Hundred Percent of Employee Contributions						3.00%
Defined Compensation Plan, Amended Employee Match Percentage on Fifty Percent of Employee Contributions						50.00%
Expense recorded relating to employee matching contribution						$ 28	$ 27	$ 25
Maximum [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Defined Compensation Plan, Amended Employee Match Percentage on Fifty Percent of Employee Contributions						5.00%
Postretirement
Pension and Other Postretirement Benefits Disclosure [Line Items]
Employer contributions						$ 9	$ 9
Percent of eligible employees who participated in voluntary buyout, more than				60.00%
Non-cash contribution charge						50
One percentage point increase effect on postretirement benefit obligation						15
One percentage point decrease effect on postretirement benefit obligation						12
Postretirement | Maximum [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Defined benefit plan effect of one percentage point increase on service and interest cost components						1
Defined benefit plan effect of one percentage point decrease on service and interest cost components						$ 1
Postretirement | Minimum [Member]
Pension and Other Postretirement Benefits Disclosure [Line Items]
Defined Compensation Plan, Amended Employee Match Percentage on One Hundred Percent of Employee Contributions						100.00%
Defined Compensation Plan, Amended Employee Match Percentage on Fifty Percent of Employee Contributions						3.00%
Pension Plans, Defined Benefit
Pension and Other Postretirement Benefits Disclosure [Line Items]
Expected contributions in 2013						$ 10
Equity Securities
Pension and Other Postretirement Benefits Disclosure [Line Items]
Targeted pension plan allocations in debt securities						70.00%	51.00%
Debt Securities
Pension and Other Postretirement Benefits Disclosure [Line Items]
Targeted pension plan allocations in debt securities						30.00%	49.00%
Forecast
Pension and Other Postretirement Benefits Disclosure [Line Items]
Employer contributions			$ 9
Non-cash contribution charge			$ 6