Income Taxes (Schedule of Reconciliation between the Statutory Federal Income Tax Rate and the Effective Tax Rate) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Differences between the statutory federal income tax rate and the effective tax rate
Provision for income taxes at statutory federal rate, Amount	$ 144	$ 120	$ 121
State income taxes, net of federal income tax benefit, Amount	13	11	11
Release of unrecognized tax benefit, Amount		(9)
Net income attributable to noncontrolling interests, Amount	(35)	(39)	(27)
Change in valuation allowance, Amount	(2)
Federal and state tax credits, Amount	(5)	(4)	(4)
nondeductible transaction costs, Amount		3
Other, Amount	1		3
Total provision for income taxes for income from continuing operations	$ 116	$ 82	$ 104
Provision for income taxes at statutory federal rate, Percentage	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit, Percentage	3.30%	3.20%	3.10%
Release of unrecognized tax benefit, Percentage		(2.60%)
Net income attributable to noncontrolling interests, Percentage	(8.60%)	(11.50%)	(7.70%)
Change in valuation allowance, Percentage	(0.40%)
Federal and state tax credits, Percentage	(1.20%)	(1.20%)	(1.10%)
Nondecutible transaction costs, Percentage		0.90%
Other, Percentage	0.30%		0.70%
Effective tax rate for income from continuing operations	28.40%	23.80%	30.00%