Deferred Policy Acquisition Costs and Value of Business Acquired Level 4 (Details) - USD ($) $ in Millions	4 Months Ended	5 Months Ended	9 Months Ended
	Sep. 30, 2018	May 31, 2018	Sep. 30, 2017	Jun. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of period	$ 421	$ 405	$ 463
Deferred costs	0	1	2
Amortization — DAC	0	(13)	(42)
Amortization — Unlock (charge) benefit, pre-tax	0	(3)	17
Adjustments to unrealized gains and losses on securities AFS and other	0	31	(14)
Balance, end of period	0	421	426
Movement in Present Value of Future Insurance Profits [Roll Forward]
Present Value of Future Insurance Profits, Net	818	0	0	$ 805	$ 0	$ 0
Present Value of Future Insurance Profits, Amortization Expense	4	0	0
Present Value of Future Insurance Profits, Amortization Expense, Assumption Change	5	0	0
Present Value of Future Insurance Profits, Unrealized Gain (Loss) on Investment	4	$ 0	$ 0
Present Value of Future Insurance Profits, Amortization Expense, Next Five Years [Abstract]
Present Value of Future Insurance Profits, Amortization Expense, Year One	6
Present Value of Future Insurance Profits, Amortization Expense, Year Two	68
Present Value of Future Insurance Profits, Amortization Expense, Year Three	63
Present Value of Future Insurance Profits, Amortization Expense, Year Four	57
Present Value of Future Insurance Profits, Amortization Expense, Year Five	$ 53