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Income Tax Expense Income Tax Expense (Effective Income Tax Rate Reconciliation) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Taxes [Line Items]      
Tax at statutory federal rate of 35 percent $ 7 $ (6) $ 65
Partnership earnings not subject to tax (126) (127) (55)
Goodwill impairment 36 55 0
Revaluation of investments in affiliates 0 0 9
State and local tax, net of federal benefit (6) 4 1
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount (225) 0 8
Other 8 2 1
Net income tax expense (benefit) $ (306) $ (72) $ 29