Income Taxes - Effective Income Tax Rate Reconciliation (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory U.S. federal income tax provision	$ 100	$ 77	$ 146
State income taxes, net of U.S. federal tax benefit	2	9	26
Foreign income tax expense	4	5	9
U.S. benefit of foreign taxes		(3)	(6)
Nontaxable liquidation of subsidiaries			(34)
Change in deferred tax asset valuation allowance	3	(2)	(3)
Change in basis difference in foreign subsidiaries		(5)	(2)
Tax rate change	(25)		(81)
Non-deductible goodwill			65
Non-deductible transaction costs		3
REIT income not subject to tax	(83)
Derecognition and remeasurement of deferred taxes	(2,347)
Other, net		(2)	(2)
Total (benefit) provision for income taxes	$ (2,346)	$ 82	$ 118