General - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Apr. 01, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Apr. 01, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Impairment of intangible assets	$ 55,000,000	$ 55,000,000	$ 0
Lease liabilities	558,000,000	558,000,000
Right-of-Use asset	$ 461,000,000	$ 461,000,000
Operating lease, renewal term	20 years	20 years
Operating lease, option to terminate		60 days
Lease, cost	$ 42,000,000	$ 83,000,000
Variable lease, cost	8,000,000	15,000,000
Stockholders' equity	(24,476,000,000)	(24,476,000,000)	(23,122,000,000)				$ (21,312,000,000)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease liabilities						$ 585,000,000
Right-of-Use asset						488,000,000
Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle				$ 0		21,000,000		$ 0		$ 1,088,000,000
Stockholders' equity	(45,803,000,000)	(45,803,000,000)	(43,997,000,000)		$ (45,148,000,000)		(44,033,000,000)		$ (43,479,000,000)		$ (41,579,000,000)
Retained income | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle						21,000,000
Accumulated other comprehensive income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle				0		0		$ 0		(910,000,000)
Stockholders' equity	$ (1,760,000,000)	$ (1,760,000,000)	(243,000,000)		(1,085,000,000)		(118,000,000)		(398,000,000)		(1,889,000,000)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, term of contract	1 year	1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, term of contract	11 years	11 years
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' equity	$ 227,000,000	$ 227,000,000	0							0
Impact of change | Impact of change | Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle				0		0				0
Stockholders' equity	1,739,000,000	1,739,000,000	1,511,000,000	18,000,000	1,670,000,000		1,675,000,000		1,552,000,000	1,580,000,000	1,583,000,000
Impact of change | Impact of change | Accumulated other comprehensive income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of change in accounting principle				0		$ 0				0
Stockholders' equity	$ (1,512,000,000)	$ (1,512,000,000)	$ (1,511,000,000)	$ (18,000,000)	$ (1,651,000,000)		$ (1,675,000,000)		$ (1,548,000,000)	$ (1,580,000,000)	$ (1,583,000,000)