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Stock-Based Compensation Plans and Employee Benefits - Summary of Fair Value of Value Sharing Equity Program Grants (Detail) - 2016 VSEP [Member]
12 Months Ended
Dec. 31, 2016
Fair Value Inputs Equity Quantitative Information [Line Items]  
Risk-free interest rate 0.80%
Weighted-average dividend yield 5.00%
Expected life 3 years
Expected volatility, minimum 17.00%
Expected volatility, maximum 19.00%