Income Taxes - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
	Dec. 22, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Tax Cuts And Jobs Act Of 2017, Provisional income tax benefit	$ 175,842
Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings	$ 78,145
Federal tax rate change		61.40%	(0.00%)	(0.00%)
Unrecognized tax benefits		$ 30,729	$ 17,268	$ 23,093	$ 26,890
Increase (decreases) in interest and penalties		553	(153)	(193)
Accrued amount for interest and penalties		1,417	864
Investment assets		185,940	233,583
Income taxes receivable in other assets primarily related to the separate state income tax returns filed by certain subsidiaries		5,845	7,819
Great West Lifeco US Inc
Income Tax Contingency [Line Items]
Income taxes receivable from Lifeco		41,694	35,093
Federal Low Income Housing tax credit carryforward
Income Tax Contingency [Line Items]
Guaranteed Federal low Income Housing tax credit carryforwards generated		120	215	$ 3,295
Total credit carryforward		142,089
Foreign investment tax credit carryforward
Income Tax Contingency [Line Items]
Guaranteed Federal low Income Housing tax credit carryforwards generated		3,474
Total credit carryforward			23,984
Minimum
Income Tax Contingency [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, amount of unrecorded benefit		8
Maximum
Income Tax Contingency [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, amount of unrecorded benefit		10
Available-for-sale Securities
Income Tax Contingency [Line Items]
Investment assets		$ 141,458	$ 172,405