Share-Based Compensation Plans - Summary of Valuation Assumptions for Incentive Performance Plan (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Performance Shares, Liability Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.88%
Volatility factor	33.01%
Expected term	2 years
Performance Share, Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.47%	1.31%	1.10%	0.78%	0.36%
Volatility factor	32.30%	28.43%	27.45%	31.38%	32.97%
Expected term	3 years	3 years	3 years	3 years	3 years