Implementation of ASU 2016-2 (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset	$ 326		$ 0
Operating lease, liability	332
Disposal group including discontinued operation, operating leased assets	20		0
Disposal group including discontinued operation, operating lease liability	$ 20		$ 0
Accounting Standards Update 2016-02
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset		$ 351
Operating lease, liability		358
Disposal group including discontinued operation, operating leased assets		19
Disposal group including discontinued operation, operating lease liability		$ 21