Property Casualty Loss And Loss Expenses (Claims Development - Homeowner) (Details) reported_claim in Thousands, $ in Millions	Dec. 31, 2018 USD ($) reported_claim	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	$ 2,588
Liabilities for loss and ALAE, net of reinsurance	5,366
Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	1,614
Cumulative paid losses and ALAE, net of reinsurance	1,474
All outstanding liabilities before, net of reinsurance	3
Liabilities for loss and ALAE, net of reinsurance	143
2014 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	284	$ 285	$ 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	$ 283	283	281	273	$ 224
2015 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	274	275	275	284
Total of incurred but not reported liabilities plus expected development on reported losses	$ 0
Cumulative number of reported claims | reported_claim	24
Cumulative paid losses and ALAE, net of reinsurance	$ 272	269	260	$ 203
2016 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	303	304	315
Total of incurred but not reported liabilities plus expected development on reported losses	$ 1
Cumulative number of reported claims | reported_claim	23
Cumulative paid losses and ALAE, net of reinsurance	$ 295	283	$ 208
2017 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	383	356
Total of incurred but not reported liabilities plus expected development on reported losses	$ 3
Cumulative number of reported claims | reported_claim	26
Cumulative paid losses and ALAE, net of reinsurance	$ 356	$ 277
2018 | Home Owner Line | Personal Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	370
Total of incurred but not reported liabilities plus expected development on reported losses	$ 15
Cumulative number of reported claims | reported_claim	21
Cumulative paid losses and ALAE, net of reinsurance	$ 268