XML 123 R106.htm IDEA: XBRL DOCUMENT v3.8.0.1
Reinsurance (Components of Written Premiums) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Effects of Reinsurance [Line Items]      
Direct premiums written $ 11,141 $ 10,946 $ 10,345
Assumed premiums written 377 297 319
Ceded premiums written 4,449 4,255 3,702
Net written premiums 7,069 6,988 6,962
Property and Casualty Insurance      
Effects of Reinsurance [Line Items]      
Direct premiums written 10,655 10,451 9,852
Assumed premiums written 327 245 270
Ceded premiums written 4,449 4,255 3,702
Net written premiums 6,533 6,441 6,420
Long term care Insurance Product Line      
Effects of Reinsurance [Line Items]      
Direct premiums written 486 495 493
Assumed premiums written 50 52 49
Ceded premiums written 0 0 0
Net written premiums $ 536 $ 547 $ 542
Percentage of assumed premiums written to net premiums written      
Effects of Reinsurance [Line Items]      
Percentage of assumed premium written to premium written net 5.30% 4.30% 4.60%
Percentage of assumed premiums written to net premiums written | Property and Casualty Insurance      
Effects of Reinsurance [Line Items]      
Percentage of assumed premium written to premium written net 5.00% 3.80% 4.20%
Percentage of assumed premiums written to net premiums written | Long term care Insurance Product Line      
Effects of Reinsurance [Line Items]      
Percentage of assumed premium written to premium written net 9.30% 9.50% 9.00%