Employee Benefit Plans - Aggregate Fair Value of CMRT Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
CMRT asset value	$ 722,764	$ 726,410
Fair value input	100.00%	100.00%
Domestic equities, principally publicly traded	100.00%	100.00%
Domestic Equities Principally Publicly Traded
Defined Benefit Plan Disclosure [Line Items]
Domestic equities, principally publicly traded	53.00%	43.00%
IEPT
Defined Benefit Plan Disclosure [Line Items]
Domestic equities, principally publicly traded		2.00%
FIPT
Defined Benefit Plan Disclosure [Line Items]
Domestic equities, principally publicly traded	35.00%	12.00%
PMLP
Defined Benefit Plan Disclosure [Line Items]
Domestic equities, principally publicly traded	11.00%	8.00%
OI
Defined Benefit Plan Disclosure [Line Items]
Domestic equities, principally publicly traded	1.00%	35.00%
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value input	79.00%	82.00%
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value input	4.00%	1.00%
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value input	17.00%	17.00%