Leases - Narrative (Details) $ in Millions		12 Months Ended
	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) building	Dec. 31, 2017 USD ($)	Dec. 31, 2019 building
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net rental expense		$ 360	$ 144
Number of office buildings | building		2
Discontinued Operations
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net rental expense		$ 23	22
ASC 842
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease assets	$ 282
Operating lease liabilities, current	(72)
Operating lease liabilities, noncurrent	(222)
Cumulative effect adjustment to increase retained earnings, net of deferred taxes	21
Deferred taxes on cumulative effect adjustment	$ 6
Sale and leaseback transactions
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of buildings under sale and leaseback transactions | building				2
Office building
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred gain on sale leaseback transaction		$ 4	$ 4