Segments - Reconciliation of Gross Margin to Consolidated Income (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total revenue	$ 4,549	$ 4,119
Add: other operating revenues	4,549	4,119
Less: other operating expenses	(4,275)	(3,839)
Operating income	274	280
Other expenses, net	21	20
Income before income tax expense	253	260
Other operating
Segment Reporting Information [Line Items]
Total revenue	245	167
Add: other operating revenues	245	167
Less: other operating expenses	(559)	(468)
Health Plans
Segment Reporting Information [Line Items]
Total revenue	4,545	4,117
Add: other operating revenues	4,545	4,117
Health Plans \| Operating Segments
Segment Reporting Information [Line Items]
Gross margin	588	581
Other
Segment Reporting Information [Line Items]
Total revenue	4	2
Add: other operating revenues	$ 4	$ 2

Total costs of sales and operating expenses for the period.

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