Insurance and Contractholder Liabilities - Integrated Medical - Prior Year Development (Details) - Integrated Medical [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Variance (unfavorable) in incurred costs related to prior years' claims payable	$ 165	$ 173	$ 227
Variance (unfavorable) in incurred costs related to prior years' claims payable, percentage	0.80%	0.90%
Favorable (unfavorable) impact of prior year development on shareholders' net income	$ 67	$ 77
Favorable (unfavorable) impact of prior year development on pre-tax income	85	97
Completion Factors [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Variance (unfavorable) in incurred costs related to prior years' claims payable	$ 90	$ 92
Variance (unfavorable) in incurred costs related to prior years' claims payable, percentage	0.40%	0.50%
Medical Cost Trend [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Variance (unfavorable) in incurred costs related to prior years' claims payable	$ 75	$ 72
Variance (unfavorable) in incurred costs related to prior years' claims payable, percentage	0.40%	0.40%
Other [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Abstract]
Variance (unfavorable) in incurred costs related to prior years' claims payable	$ 0	$ 9
Variance (unfavorable) in incurred costs related to prior years' claims payable, percentage	0.00%	0.00%