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Income Taxes Level 4 Effective Income Tax Rate Reconciliation (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Jun. 30, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Income Tax Contingency [Line Items]                
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 89 $ 185 $ 211 $ 378        
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount (31) (31) (91) (94)        
Effective Income Tax Rate Reconciliation, Deduction, Dividends, Amount (37) (14) (75) (57)        
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount 0 0 0 78        
Effective Income Tax Rate Reconciliation, Disposition of Business, Amount 0 (50) 5 (50)        
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount 5 0 (6) 3        
Provision for income taxes 22 90 32 102        
Unrecognized Tax Benefits 15 12 15 12 $ 12 $ 12 $ 12 $ 12
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions 3 0 3 0        
Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions 0 0 $ 0 0        
Income Tax Examination, Description     The federal audit of the years 2012 and 2013 was completed as of March 31, 2017 with no additional adjustments. The federal audit of The Company's recently acquired subsidiary Maxum for the 2014 tax year is expected to be completed in the fourth quarter of 2017 with no significant adjustments. Management believes that adequate provision has been made in the consolidated financial statements for any potential adjustments that may result from tax examinations and other tax-related matters for all open tax years.          
Stock-based Compensation [Member]                
Income Tax Contingency [Line Items]                
Effective Income Tax Rate Reconciliation, Deduction, Employee Stock Ownership Plan Dividend, Amount $ (4) $ 0 $ (12) $ 0