Income Taxes Effective Income Tax Rate Reconciliation (Details)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Expected federal statutory income tax rate		35.00%	35.00%	35.00%
Increase/(decrease)
Federal rate adjustment to deferred taxes	[1]	(20.20%)
State and local income taxes, net of federal benefit		1.90%	1.70%	1.80%
Other		(0.30%)	(0.40%)	0.90%
Effective tax rate (excluding noncontrolling interests)		16.40%	36.30%	37.70%
Income attributable to noncontrolling interests		(0.20%)	(1.30%)	(0.30%)
Effective tax rate per Consolidated Statements of Income		16.20%	35.00%	37.40%

[1] Represents the impact of revaluing the net deferred tax liability due to the enactment of the Tax Act, and includes the federal tax benefit of any state and local deferred taxes.