Business Segments (Corporate Items) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues - divested businesses		$ 1,096	$ 964	$ 3,197	$ 3,141
Expenses:
Amortization expense of acquired intangible assets		25	27	76	83
Merger and strategic initiatives expense		10	6	25	7
Restructuring charges		30	0	30	0
Clearing default loss	$ 8
Operating income		226	246	757	787
Corporate Items
Segment Reporting Information [Line Items]
Revenues - divested businesses		0	10	10	87
Expenses:
Amortization expense of acquired intangible assets		25	27	76	83
Merger and strategic initiatives expense		10	6	25	7
Restructuring charges		30	0	30	0
Provision for notes receivable		20	0	20	0
Clearing default loss		0	8	0	8
Extinguishment of debt		0	0	11	0
Expenses - divested businesses		0	8	8	75
Other		4	2	10	8
Total expenses		89	51	180	181
Operating income		$ (89)	$ (41)	$ (170)	$ (94)