Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Excluding Hardy - International $ in Millions	Dec. 31, 2019 USD ($) claim	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,892
IBNR	623
2010
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	187	$ 190	$ 194	$ 200	$ 207	$ 213	$ 223	$ 228	$ 234	$ 238
IBNR	$ 6
Cumulative Number of Claims | claim	21,952
2011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 214	221	224	226	233	244	264	272	$ 271
IBNR	$ 3
Cumulative Number of Claims | claim	24,589
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 236	242	249	256	256	264	279	$ 272
IBNR	$ 19
Cumulative Number of Claims | claim	24,978
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 246	255	263	267	287	295	$ 294
IBNR	$ 18
Cumulative Number of Claims | claim	23,932
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 294	277	285	297	297	$ 282
IBNR	$ 31
Cumulative Number of Claims | claim	24,912
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 286	292	310	311	$ 296
IBNR	$ 37
Cumulative Number of Claims | claim	23,305
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 292	294	309	$ 290
IBNR	$ 59
Cumulative Number of Claims | claim	17,626
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 393	371	$ 306
IBNR	$ 133
Cumulative Number of Claims | claim	18,176
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 394	$ 376
IBNR	$ 132
Cumulative Number of Claims | claim	19,756
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 350
IBNR	$ 185
Cumulative Number of Claims | claim	13,415