Income Taxes - Summary of Effective Tax Rates (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax provision (benefit) at the U.S. federal statutory income tax rate										$ (285)	$ (303)	$ 270
State and local taxes, net of Federal benefit										(11)	(14)	12
Adjustment with respect to tax for prior periods	[1]									33	(16)	38
Adjustment of tax rate used to value deferred taxes	[2]									6	(40)	(52)
Change in valuation allowance	[3]									29	(90)	(28)
Uncertain tax positions	[4]									(24)	(4)	(2)
Other non-deductible/non-taxable items	[5]									(7)	(4)	(11)
Other										1	0	(3)
Total income tax expense (benefit)		$ 64	$ (203)	$ (63)	$ (56)	$ (114)	$ (129)	$ (200)	$ (28)	$ (258)	$ (471)	$ 224
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Tax benefit at the U.S. federal statutory income tax rate, percent										35.00%	35.00%	35.00%
State and local taxes, net of Federal benefit, percent										1.30%	1.60%	1.60%
Adjustment with respect to tax for prior periods, percent	[1]									(4.00%)	1.80%	4.90%
Adjustment of tax rate used to value deferred taxes, percent	[2]									(0.80%)	4.60%	(6.70%)
Change in valuation allowance, percent	[3]									(3.60%)	10.40%	(3.60%)
Uncertain tax positions, percent	[4]									3.00%	0.50%	(0.30%)
Other non-deductible/non-taxable items, percent	[5]									0.80%	0.50%	(1.40%)
Other, percent										0.00%	0.10%	(0.40%)
Total income tax expense (benefit), percent										31.70%	54.50%	29.10%
Adjustment related to the Federal audit of the 2013 tax year		$ 12								$ 12
Out of period adjustment to the deferred tax asset balance										$ 15
State and Local Jurisdiction [Member] | Minimum [Member]
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
NOL Carryforward period												12 years
State and Local Jurisdiction [Member] | Maximum [Member]
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
NOL Carryforward period												20 years

[1] For 2016, the amounts were impacted by a $12 million adjustment related to the Federal audit of the 2013 tax year as well as the impact of a reversal of approximately $15 million associated with an out of period adjustment to our deferred tax asset balance. For 2015, the amount relates to an adjustment to a deferred tax balance sheet account as a result of the Federal audit for the 2012 tax year. For 2014, the amount relates to changes in estimates as a result of filing the Federal and State income tax returns and a change in State tax expense as a result of filing amended State tax returns upon the closing of the Federal audits for the 2006 - 2009 tax years.

[2] For 2016, the amount largely relates to the effect of revaluing our deferred tax assets based on the recently filed tax returns. For 2015, the amount mainly relates to the effects of revaluing our deferred tax assets for New York City Tax Reform that was enacted on April 13, 2015. For 2014, the amount primarily relates to the effects of revaluing our deferred tax assets as a result of New York State Tax Reform that was enacted on March 31, 2014.

[3] For 2016, the amounts primarily reflect an increase in valuation allowance reserves on certain state net operating loss carryforwards. For 2015, the amount is due to the release of valuation allowance reserves on previously unrecognized State net operating loss carryforwards and temporary differences. For 2014, the amount relates to changes in valuation allowance reserves in States with net operating loss carryforward periods of 12 to 20 years and a release of valuation allowance reserves as a result of filing amended State tax returns upon the closing of the Federal audits for the 2006-2009 tax years.

[4] For 2016, the amount primarily relates to the resolution of an uncertain items related to the Federal Audit of the 2013 tax year. The amount for 2016 also reflects the conclusion of certain State audits. For 2015 and 2014, the amounts primarily relate to the conclusion of State audits and expiration of State statutes of limitations.

[5] For 2016, 2015 and 2014, the amount primarily relates to tax exempt income and, for 2015 and 2014, nondeductible penalties.