General - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 23,418,000,000		$ 21,312,000,000	$ 23,273,000,000
Lease liabilities	572,000,000
Right-of-Use asset	474,000,000
Operating lease, cost	41,000,000
Variable lease, cost	$ 7,000,000
Operating lease, renewal term	14 years
Operating lease, option to terminate	60 days
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]
Stockholders' Equity Attributable to Parent	$ 45,148,000,000		44,033,000,000	43,479,000,000		$ 41,579,000,000
Cumulative effect of change in accounting principle		21,000,000			$ 1,088,000,000
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]
Stockholders' Equity Attributable to Parent	$ 1,085,000,000		118,000,000	398,000,000		1,889,000,000
Cumulative effect of change in accounting principle		0			(910,000,000)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, term of contract	1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, term of contract	11 years
Adjustment | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ (19,000,000)	0		(4,000,000)
Adjustment | Impact of change | Retained income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	(1,670,000,000)		(1,675,000,000)	(1,552,000,000)		(1,583,000,000)
Cumulative effect of change in accounting principle		0			0
Adjustment | Impact of change | Accumulated other comprehensive income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Stockholders' Equity Attributable to Parent	$ 1,651,000,000	1,580,000,000	$ 1,675,000,000	$ 1,548,000,000		$ 1,583,000,000
Cumulative effect of change in accounting principle		$ 0			$ 0