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Shareholders' Equity And Dividend Restrictions (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Declared cash dividends, per share $ 2.50 $ 1.92 $ 2.3
Dividends declared by insurance subsidiary to parent $ 465 $ 475 $ 447
Dividend payment without prior regulatory approval, maximum percent of policyholder surplus 10.00%    
Dividend payment without prior regulatory approval, percent of statutory net income for the prior calendar year 100.00%    
Dividends might be paid during next year $ 509    
Accumulated Other Comprehensive Income | New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2018-02      
Adjustment to reclassify certain tax effects from AOCI to retained earnings 492 0 0
Retained Earnings | New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2018-02      
Adjustment to reclassify certain tax effects from AOCI to retained earnings $ (492) $ 0 $ 0