Quarterly Financial Information - Shareholders’ Equity (As Restated) (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	$ 5,672	$ 6,005	$ 5,728	$ 5,286	$ 4,915				$ 5,728	$ 6,005	$ 5,672	$ 4,915	$ 5,069	$ 5,265
Net income attributable to the controlling and noncontrolling interests	156	616	501	342	344	$ (179)	$ 376	$ 354	843	1,459	1,615	895	1,427
Other comprehensive loss, net of tax		(2)	23	287					310	308	316	336	(599)
Dividends, Common Stock, Cash				(103)					(205)	(321)	(434)	(414)	(383)
Issuance of treasury stock				34					49	75	83	55	71
Stock Repurchased During Period, Value				(163)					(163)	(413)
Stock-based compensation activity				(21)					(16)	(8)		35	46
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders										(5)	(5)	(4)	(4)
Stockholders' Equity, Other				(5)					(5)	(5)
Parent
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	5,557	5,897	5,623	5,192	4,828				5,623	5,897	5,557	4,828	4,983	5,180
Net income attributable to the controlling and noncontrolling interests				337					833	1,443	1,594	873	1,406
Other comprehensive loss, net of tax				280					297	293	299	346	(586)
Dividends, Common Stock, Cash				(103)					(205)	(321)	(434)	(414)	(383)
Issuance of treasury stock				34					49	75	83	55	71
Stock Repurchased During Period, Value				(163)					(163)	(413)
Stock-based compensation activity				(21)					(16)	(8)		35	46
Stockholders' Equity, Other				0					0	0
Non-controlling Interests
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	115	$ 108	$ 105	94	87				105	108	115	87	86	85
Net income attributable to the controlling and noncontrolling interests				5					10	16	21	22	21
Other comprehensive loss, net of tax				7					13	15	17	(10)	(13)
Dividends, Common Stock, Cash				0					0	0
Issuance of treasury stock				0					0	0
Stock Repurchased During Period, Value				0					0	0
Stock-based compensation activity				0					0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders										(5)	(5)	(4)	(4)
Stockholders' Equity, Other				$ (5)					$ (5)	$ (5)
Common Stock
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest	$ 969				$ 969						$ 969	$ 969	$ 969	$ 484