Property Casualty Loss And Loss Expenses (Claims Development - Homeowner) (Details) reported_claim in Thousands, $ in Millions	Dec. 31, 2016 USD ($) reported_claim	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	$ 2,187
Liabilities for loss and ALAE, net of reinsurance	4,770
Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	1,452
Cumulative paid losses and ALAE, net of reinsurance	1,322
All outstanding liabilities before, net of reinsurance	2
Liabilities for loss and ALAE, net of reinsurance	132
2012 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	329	$ 330	$ 328	$ 330	$ 344
Total of incurred but not reported liabilities plus expected development on reported losses	$ 0
Cumulative number of reported claims | reported_claim	33
Cumulative paid losses and ALAE, net of reinsurance	$ 329	328	324	317	$ 256
2013 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	247	247	246	252
Total of incurred but not reported liabilities plus expected development on reported losses	$ 0
Cumulative number of reported claims | reported_claim	25
Cumulative paid losses and ALAE, net of reinsurance	$ 244	242	236	$ 180
2014 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	286	283	297
Total of incurred but not reported liabilities plus expected development on reported losses	$ 0
Cumulative number of reported claims | reported_claim	26
Cumulative paid losses and ALAE, net of reinsurance	$ 281	273	$ 224
2015 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	275	284
Total of incurred but not reported liabilities plus expected development on reported losses	$ 3
Cumulative number of reported claims | reported_claim	23
Cumulative paid losses and ALAE, net of reinsurance	$ 260	$ 203
2016 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	315
Total of incurred but not reported liabilities plus expected development on reported losses	$ 29
Cumulative number of reported claims | reported_claim	21
Cumulative paid losses and ALAE, net of reinsurance	$ 208