Reserves for Future Policy Benefits and Contract Owner Account Balances - Contract Owner Account Balances (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contract owner account balances	$ 50,158	$ 50,273
Universal life-type contracts
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contract owner account balances	14,561	14,626
Fixed annuities and payout contracts without life contingencies
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contract owner account balances	34,949	35,014
GICs and other
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contract owner account balances	$ 648	$ 633