Retirement Plans - Changes in Financial Assets that are Measured at Fair Value Based on Level 3 Inputs that are held by Institutional Funds (Detail) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	$ 457	$ 430
Actual return on plan assets	22	24
Purchases, sales or other settlements	(86)	3
Net transfers in (out) of Level 3	0	0
Ending balance	393	457
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	2	3
Actual return on plan assets	0	0
Purchases, sales or other settlements	1	(1)
Net transfers in (out) of Level 3	0	0
Ending balance	3	2
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	302	291
Actual return on plan assets	(5)	9
Purchases, sales or other settlements	(81)	2
Net transfers in (out) of Level 3	0	0
Ending balance	216	302
Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	105	89
Actual return on plan assets	18	15
Purchases, sales or other settlements	(1)	1
Net transfers in (out) of Level 3	0	0
Ending balance	122	105
Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	48	47
Actual return on plan assets	9	0
Purchases, sales or other settlements	(5)	1
Net transfers in (out) of Level 3	0	0
Ending balance	$ 52	$ 48