Pension and Other Postretirement Benefits - Schedule of Benefit Payments Expected to be Paid and Expected Medicare Part D Subsidy Receipts (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2014	$ 880
2015	880
2016	900
2017	910
2018	920
2019 through 2023	4,680
Total benefit payments	9,170
Gross Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2014	260
2015	260
2016	260
2017	255
2018	255
2019 through 2023	1,195
Total benefit payments	2,485
Medicare Part D Subsidy Receipts [Member]
Defined Benefit Plan Disclosure [Line Items]
2014	25
2015	25
2016	25
2017	30
2018	30
2019 through 2023	145
Total benefit payments	280
Net Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2014	235
2015	235
2016	235
2017	225
2018	225
2019 through 2023	1,050
Total benefit payments	$ 2,205