Discontinued Operations - Income Statement (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Expenses
Net income from discontinued operations	$ 69	$ (2)	$ 1	$ 6	$ (29)	$ (4)	$ 821	$ 40	$ 74	$ 828	$ 177
Tempo Business | Discontinued Operations
Revenue
Total revenue									0	698	2,218
Expenses
Total operating expenses									12	656	1,950
Operating Income from discontinued operations									(12)	42	268
Other income									0	10	0
Income from discontinued operations before income taxes									(12)	52	268
Income tax expense (benefit)									(4)	3	91
Net income (loss) from discontinued operations, excluding gain									(8)	49	177
Gain on sale of discontinued operations, net of tax									82	779	0
Net income from discontinued operations									$ 74	$ 828	$ 177