Employee Benefit Plans - Schedule of Asset Allocation Strategy (Detail)	12 Months Ended
	Dec. 31, 2014
Domestic Equities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	14.00%
Asset Allocation Strategy, Maximum Allocation Percentage	32.00%
Foreign Equities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	13.00%
Asset Allocation Strategy, Maximum Allocation Percentage	25.00%
Fixed Income
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	26.00%
Asset Allocation Strategy, Maximum Allocation Percentage	40.00%
Alternative Strategies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	6.00%
Asset Allocation Strategy, Maximum Allocation Percentage	14.00%
Diversifying Assets
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	7.00%
Asset Allocation Strategy, Maximum Allocation Percentage	19.00%
Cash
Schedule of Trading Securities and Other Trading Assets [Line Items]
Asset Allocation Strategy, Minimum Allocation Percentage	0.00%
Asset Allocation Strategy, Maximum Allocation Percentage	5.00%