INCOME TAXES - EFFECTIVE INCOME TAX RECONCILIATION (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
U.S. federal tax rate	35.00%	35.00%	35.00%
Income before income tax	$ 975	$ 816	$ 514
Expected tax expense	341	286	180
Nondeductible expenses	4	4	3
State income taxes	25	21	14
Other—net	0	(3)	1
Total tax expense related to income	$ 370us-gaap_IncomeTaxExpenseBenefit	$ 308us-gaap_IncomeTaxExpenseBenefit	$ 198us-gaap_IncomeTaxExpenseBenefit
Effective tax rate	37.90%	37.70%	38.50%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority noncontrolling interest income (loss), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, increase (decrease) in enacted tax rate, prior year income taxes, increase (decrease) in deferred tax asset valuation allowance, and other adjustments.

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