Schedule IV - Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Premiums:
Ceded to other companies, premiums	$ 103	$ 131	$ 310	$ 380
Net amount	$ 8,030	$ 7,605	$ 24,143	$ 23,005