Employee Benefit Plans - Schedule of Aggregate Fair Value of Asset and Supplemental Asset Mix (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
CMRT asset value	$ 722.8	$ 726.4
CMRT fair value input	100.00%	100.00%
CMRT asset mix	100.00%	100.00%
Level 1
Defined Benefit Plan Disclosure [Line Items]
CMRT fair value input	79.00%	82.00%
Level 2
Defined Benefit Plan Disclosure [Line Items]
CMRT fair value input	4.00%	1.00%
Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
CMRT fair value input	17.00%	17.00%
Domestic Equities, Principally Publicly Traded
Defined Benefit Plan Disclosure [Line Items]
CMRT asset mix	53.00%	43.00%
International Equities, Publicly Traded
Defined Benefit Plan Disclosure [Line Items]
CMRT asset mix		2.00%
Fixed Income Securities, Publicly Traded
Defined Benefit Plan Disclosure [Line Items]
CMRT asset mix	35.00%	12.00%
Privately Managed Limited Partnerships
Defined Benefit Plan Disclosure [Line Items]
CMRT asset mix	11.00%	8.00%
Other Assets
Defined Benefit Plan Disclosure [Line Items]
CMRT asset mix	1.00%	35.00%