Segments - Reconciliation of Gross Margin to Consolidated Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total revenue	$ 4,243	$ 4,697	$ 12,555	$ 14,226
Add: other operating revenues	4,243	4,697	12,555	14,226
Add: gain on sale of subsidiary	0	37	0	37
Less: other operating expenses	(3,986)	(4,439)	(11,753)	(13,404)
Operating income	257	295	802	859
Other expenses, net	24	36	52	116
Income before income tax expense	233	259	750	743
Operating Segments
Segment Reporting Information [Line Items]
Gross margin	561	566	1,725	1,854
Other operating
Segment Reporting Information [Line Items]
Total revenue	159	230	470	661
Add: other operating revenues	159	230	470	661
Add: gain on sale of subsidiary	0	37	0	37
Less: other operating expenses	(463)	(538)	(1,393)	(1,693)
Health Plans
Segment Reporting Information [Line Items]
Total revenue	4,239	4,565	12,546	13,826
Add: other operating revenues	4,239	4,565	12,546	13,826
Health Plans \| Operating Segments
Segment Reporting Information [Line Items]
Gross margin	561	547	1,725	1,812
Other
Segment Reporting Information [Line Items]
Total revenue	4	132	9	400
Add: other operating revenues	4	132	9	400
Other \| Operating Segments
Segment Reporting Information [Line Items]
Gross margin	$ 0	$ 19	$ 0	$ 42

Total costs of sales and operating expenses for the period.

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