Insurance and Contractholder Liabilities - Integrated Medical - Activity (Details) - Integrated Medical [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Medical Claims Payable Activity [Abstract]
Beginning balance, unpaid claims, gross	$ 2,420	$ 2,261	$ 2,105
Less: Reinsurance and other amounts recoverable	262	273	237
Beginning balance, unpaid claims, net	2,158	1,988	1,868
Acquired net:	40	0	0
Incurred claims related to:
Current year	21,331	19,334	18,085
Prior years	(173)	(227)	(70)
Total incurred	21,158	19,107	18,015
Paid claims related to:
Current year	18,978	17,179	16,142
Prior years	1,945	1,758	1,753
Total paid	20,923	18,937	17,895
Ending balance, unpaid claims, net	2,433	2,158	1,988
Add: Reinsurance and other amounts recoverable	264	262	273
Ending balance, unpaid claims, gross	$ 2,697	$ 2,420	$ 2,261