Reserve for Future Policy Benefits and SA Liabilities Level 4 Changes in Reserve for Future Policy Benefits (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 in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	$ 18,292	$ 14,308	$ 14,280	$ 18,057	$ 14,482	$ 14,000
Liabilities for Guarantees on Long-Duration Contracts, Incurred Benefits	557	402	811
Liabilities for Guarantees on Long-Duration Contracts, Payment for Benefits	(322)	(371)	(666)
Liabilities for Guarantees on Long-Duration Contracts, Other Liability Adjustments		(205)	135
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	18,292	14,308	14,280	18,057	14,482	14,000
Movement in Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	8,471	5,213	4,949	5,315	5,146	4,756
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable, Incurred Benefits, Net	3,203	128	301
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverables, Payment for Benefits, Net	(47)	(61)	(108)
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	8,471	5,213	4,949	5,315	5,146	4,756
Guaranteed Minimum Death Benefit [Member]
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	466	884	767	471	873	786
Liabilities for Guarantees on Long-Duration Contracts, Incurred Benefits	29	56	57
Liabilities for Guarantees on Long-Duration Contracts, Payment for Benefits	(34)	(45)	(76)
Liabilities for Guarantees on Long-Duration Contracts, Other Liability Adjustments		0	0
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	466	884	767	471	873	786
Movement in Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	286	463	406	294	464	432
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable, Incurred Benefits, Net	20	36	37
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverables, Payment for Benefits, Net	(28)	(37)	(63)
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	286	463	406	294	464	432
Secondary Guarantees [Member] | Universal Life [Member]
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	3,196	3,057	2,858	3,057	2,940	2,627
Liabilities for Guarantees on Long-Duration Contracts, Incurred Benefits	139	117	231
Liabilities for Guarantees on Long-Duration Contracts, Other Liability Adjustments		0	0
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	3,196	3,057	2,858	3,057	2,940	2,627
Movement in Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	3,196	3,057	2,858	3,057	2,940	2,627
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable, Incurred Benefits, Net	139	117	231
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	3,196	3,057	2,858	3,057	2,940	2,627
Annuitization Benefit [Member]
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	14,630	10,367	10,655	14,529	10,669	10,587
Liabilities for Guarantees on Long-Duration Contracts, Incurred Benefits	389	229	523
Liabilities for Guarantees on Long-Duration Contracts, Payment for Benefits	(288)	(326)	(590)
Liabilities for Guarantees on Long-Duration Contracts, Other Liability Adjustments		(205)	135
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross	14,630	10,367	10,655	14,529	10,669	10,587
Movement in Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable [Roll Forward]
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	4,989	1,693	1,685	1,964	1,742	1,697
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable, Incurred Benefits, Net	3,044	(25)	33
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverables, Payment for Benefits, Net	(19)	(24)	(45)
Liabilities for Guarantees on Long-Duration Contracts, Reinsurance Recoverable	$ 4,989	$ 1,693	$ 1,685	$ 1,964	$ 1,742	$ 1,697