Supplemental Condensed Consolidating Financial Information and Other Collateral-Related Information - Summary of Restatement Adjustments to Financial Statements (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Adjustments or Reclassifications [Line Items]
Goodwill and other intangible assets	$ 7,394	$ 6,704	$ 6,731	$ 6,416
Property and equipment, net	17,895	16,352
Subsidiary Guarantors [Member]
Adjustments or Reclassifications [Line Items]
Goodwill and other intangible assets	4,893	4,612
Property and equipment, net	11,110	10,464
Intercompany balances	(25,228)	(22,495)
Subsidiary Guarantors [Member] | Adjustment [Member]
Adjustments or Reclassifications [Line Items]
Goodwill and other intangible assets		2,884
Property and equipment, net		2,001
Subsidiary Non-Guarantors [Member]
Adjustments or Reclassifications [Line Items]
Goodwill and other intangible assets	2,501	2,092
Property and equipment, net	6,785	5,888
Intercompany balances	$ (352)	(1,012)
Subsidiary Non-Guarantors [Member] | Adjustment [Member]
Adjustments or Reclassifications [Line Items]
Goodwill and other intangible assets		2,884
Property and equipment, net		2,001
Intercompany balances		$ 3,952