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, 2020 USD ($) claim	Dec. 31, 2019 USD ($)	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 ($)	Dec. 31, 2011 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 3,218
IBNR	714
2011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	221	$ 223	$ 230	$ 233	$ 235	$ 242	$ 254	$ 275	$ 283	$ 282
IBNR	$ (1)
Cumulative Number of Claims | claim	24,526
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 242	246	252	259	267	267	275	290	$ 283
IBNR	$ 12
Cumulative Number of Claims | claim	24,901
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 252	256	265	274	278	299	307	$ 305
IBNR	$ 10
Cumulative Number of Claims | claim	23,808
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 308	306	288	296	309	309	$ 293
IBNR	$ 21
Cumulative Number of Claims | claim	24,601
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 301	298	304	322	324	$ 307
IBNR	$ 35
Cumulative Number of Claims | claim	22,675
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 294	304	307	322	$ 302
IBNR	$ 37
Cumulative Number of Claims | claim	15,363
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 399	407	385	$ 318
IBNR	$ 99
Cumulative Number of Claims | claim	16,086
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 416	411	$ 393
IBNR	$ 105
Cumulative Number of Claims | claim	20,423
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 379	$ 365
IBNR	$ 124
Cumulative Number of Claims | claim	16,890
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 406
IBNR	$ 272
Cumulative Number of Claims | claim	10,498