Property Casualty Loss And Loss Expenses (Claims Development - Commercial Property) (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
Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	2,588
Cumulative paid losses and ALAE, net of reinsurance	2,287
All outstanding liabilities before, net of reinsurance	13
Liabilities for loss and ALAE, net of reinsurance	314
2014 | Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	442	$ 442	$ 441	$ 444	$ 452
Total of incurred but not reported liabilities plus expected development on reported losses	$ 1
Cumulative number of reported claims | reported_claim	17
Cumulative paid losses and ALAE, net of reinsurance	$ 440	437	432	412	$ 297
2015 | Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	415	416	414	454
Total of incurred but not reported liabilities plus expected development on reported losses	$ 4
Cumulative number of reported claims | reported_claim	17
Cumulative paid losses and ALAE, net of reinsurance	$ 411	407	388	$ 279
2016 | Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	541	551	590
Total of incurred but not reported liabilities plus expected development on reported losses	$ 4
Cumulative number of reported claims | reported_claim	17
Cumulative paid losses and ALAE, net of reinsurance	$ 528	504	$ 358
2017 | Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	560	587
Total of incurred but not reported liabilities plus expected development on reported losses	$ 12
Cumulative number of reported claims | reported_claim	18
Cumulative paid losses and ALAE, net of reinsurance	$ 522	$ 395
2018 | Commercial Property Line | Commercial Insurance
Claims Development [Line Items]
Incurred losses and ALAE, net of reinsurance	630
Total of incurred but not reported liabilities plus expected development on reported losses	$ 13
Cumulative number of reported claims | reported_claim	16
Cumulative paid losses and ALAE, net of reinsurance	$ 386