Condensed Financial Information of Registrant - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 2,452	$ 2,826	$ 3,186
Investments	1,946	1,681
Receivables	1,406	1,330
Prepaid expenses and other current assets	134	149
Derivative asset	29	476
Total current assets	5,967	6,462
Property, equipment, and capitalized software, net		241
Goodwill and intangible assets, net	172	190	255
Deferred income taxes	79	117
Total assets	6,787	7,154	8,471
Current liabilities:
Medical claims and benefits payable	1,854	1,961	2,192	$ 1,929
Accounts payable and accrued liabilities	455	390
Current portion of long-term debt	18	241
Derivative liability	29	476
Total current liabilities	3,269	4,246
Long-term debt	1,237	1,020
Finance lease liabilities	231
Finance lease liabilities		197
Other long-term liabilities	90	44
Total liabilities	4,827	5,507
Stockholders’ equity:
Common stock, $0.001 par value; 150 million shares authorized; outstanding: 62 million shares at each of December 31, 2019, and December 31, 2018	0	0
Preferred stock, $0.001 par value; 20 million shares authorized, no shares issued and outstanding	0	0
Additional paid-in capital	175	643
Accumulated other comprehensive income (loss)	4	(8)
Retained earnings	1,781	1,012
Total stockholders’ equity	1,960	1,647	$ 1,337	$ 1,649
Total liabilities and stockholders’ equity	6,787	7,154
Parent Company
Current assets:
Cash and cash equivalents	836	70
Investments	161	100
Receivables	2	2
Due from affiliates	49	90
Prepaid expenses and other current assets	46	47
Derivative asset	29	476
Total current assets	1,123	785
Property, equipment, and capitalized software, net	327	176
Goodwill and intangible assets, net	13	13
Investments in subsidiaries	2,225	2,768
Deferred income taxes	10	39
Advances to related parties and other assets	76	40
Total assets	3,774	3,821
Current liabilities:
Medical claims and benefits payable	0	4
Accounts payable and accrued liabilities	260	223
Current portion of long-term debt	18	241
Derivative liability	29	476
Total current liabilities	307	944
Long-term debt	1,237	1,020
Finance lease liabilities	231
Finance lease liabilities		197
Other long-term liabilities	39	13
Total liabilities	1,814	2,174
Stockholders’ equity:
Common stock, $0.001 par value; 150 million shares authorized; outstanding: 62 million shares at each of December 31, 2019, and December 31, 2018	0	0
Preferred stock, $0.001 par value; 20 million shares authorized, no shares issued and outstanding	0	0
Additional paid-in capital	175	643
Accumulated other comprehensive income (loss)	4	(8)
Retained earnings	1,781	1,012
Total stockholders’ equity	1,960	1,647
Total liabilities and stockholders’ equity	$ 3,774	$ 3,821