Income Tax Level 4 Income tax expense (benefit) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Credit Carryforward [Line Items]
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act of 2017, Amount	$ 396,000,000	$ 0	$ 0
Current Federal Tax Expense (Benefit)	4,000,000	2,000,000	36,000,000
Deferred Federal Income Tax Expense (Benefit)	418,000,000	72,000,000	(6,000,000)
Tax Cuts and Jobs Act of 2017, Deferred Tax Asset, Income Tax Expense (Benefit)	379
Tax Cuts and Jobs Act of 2017, Deferred Tax Asset, Income Tax Expense (Benefit), Sequestration Fee Payable	17
Tax Cuts and Jobs Act of 2017, Reclassification of Deferred Income Tax Assets Into Income Taxes Receivable Payable	234
Income Tax Expense (Benefit)	$ 422,000,000	$ 74,000,000	$ 30,000,000