Income Taxes - Temporary Differences (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal and state loss carryforwards	$ 1,030	$ 1,525
Investments	1,440	2,531
Compensation and benefits	369	548
Other assets	330	397
Total gross assets before valuation allowance	3,169	5,001
Less: Valuation allowance	653	964
Assets, net of valuation allowance	2,516	4,037
Net unrealized investment gains	(824)	(980)
Insurance reserves	(342)	(301)
Deferred policy acquisition costs	(556)	(1,151)
Other liabilities	(13)	(35)
Total gross liabilities	(1,735)	(2,467)
Net deferred income tax asset (liability)	$ 781	$ 1,570