Insurance (Separate Accounts - Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Separate Accounts [Line Items]
Separate account assets	$ 205,001	$ 195,578
Gain (Loss) Recognized on Assets Transferred to Separate Account	$ 0	$ 0	$ 0
Participating Policies as Percentage of Gross Insurance in Force	3.00%	4.00%
Funding Agreements and Participating Close Out Contracts Included in Separate Accounts with a Guaranteed Minimum Return or Account Value
Schedule Separate Accounts [Line Items]
Average interest rate credited on separate accounts with a guaranteed minimum return or account value	2.34%	2.35%
Pass Through Separate Accounts
Schedule Separate Accounts [Line Items]
Separate account assets	$ 148,200	$ 134,500
Separate Accounts With Minimum Return Or Account Value
Schedule Separate Accounts [Line Items]
Separate account assets	$ 56,800	$ 61,100