Components of Equity (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stockholders Equity Note [Line Items]
Beginning Balance			$ 7,566
NET INCOME ATTRIBUTABLE TO REPORTING ENTITY	$ 368	$ 322	840	$ 784
Other comprehensive income/(loss)	(6)	3	(3)	(5)
Ending Balance	7,505		7,505
Common Stock
Stockholders Equity Note [Line Items]
Beginning Balance	7	7	7	7
Ending Balance	7	7	7	7
Additional Paid-in Capital
Stockholders Equity Note [Line Items]
Beginning Balance	7,948	8,100	8,156	8,097
Issuance of common stock for comprehensive stock plans, net	4	4	6	10
Repurchase of common stock	(200)		(400)
Changes in ownership and other	10	4		1
Ending Balance	7,762	8,108	7,762	8,108
Accumulated Other Comprehensive Income (Loss)
Stockholders Equity Note [Line Items]
Beginning Balance	(56)	(68)	(59)	(60)
Other comprehensive income/(loss)	(6)	3	(3)	(5)
Ending Balance	(62)	(65)	(62)	(65)
Retained Earnings / (Deficit)
Stockholders Equity Note [Line Items]
Beginning Balance	(432)	(901)	(610)	(1,071)
NET INCOME ATTRIBUTABLE TO REPORTING ENTITY	368	322	840	784
Dividends declared on common stock	(144)	(149)	(438)	(445)
Cumulative effect of accounting change		4		4
Ending Balance	(208)	(728)	(208)	(728)
Non-redeemable, non-controlling interests
Stockholders Equity Note [Line Items]
Beginning Balance	7	28	72	29
Net income attributable to non-controlling interests		53	2	53
Distributions to non-controlling interests	(1)		(68)	(1)
Changes in ownership and other		(8)		(8)
Ending Balance	6	73	6	73
Redeemable, non-controlling interests
Stockholders Equity Note [Line Items]
Beginning Balance	141	173	128	167
Net income	4	3	9	8
Distributions to non-controlling interests	(2)	(2)	(5)	(5)
Changes in ownership and other	(10)	(4)	1
Ending Balance	$ 133	$ 170	$ 133	$ 170