Claim and Claim Adjustment Expense Reserves (International - Hardy - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - 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 ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 2,000
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	526
IBNR	275
2011
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Allocated Claim Adjustment Expense Reserves at Acquisition									$ 130
Incurred claims and allocated claim adjustment expense, net	147	$ 146	$ 146	$ 144	$ 143	$ 144	$ 139	$ 140	(2)
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented									128
IBNR	$ (1)
Cumulative Number of Claims | claim	6,307
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Net Claim and Allocated Claim Adjustment Expense Reserves at Acquisition									34
Incurred claims and allocated claim adjustment expense, net	$ 115	117	118	116	115	122	114	106	72
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented									$ 106
IBNR	$ (1)
Cumulative Number of Claims | claim	6,970
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 147	147	147	143	142	140	149	$ 133
IBNR	$ 2
Cumulative Number of Claims | claim	7,744
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 173	175	174	173	180	186	$ 188
IBNR	$ 0
Cumulative Number of Claims | claim	8,302
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 182	181	182	181	183	$ 194
IBNR	$ (5)
Cumulative Number of Claims | claim	9,401
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 230	228	240	252	$ 233
IBNR	$ 12
Cumulative Number of Claims | claim	10,369
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 247	246	258	$ 248
IBNR	$ 5
Cumulative Number of Claims | claim	12,430
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 314	310	$ 278
IBNR	$ 44
Cumulative Number of Claims | claim	14,076
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 229	$ 226
IBNR	$ 76
Cumulative Number of Claims | claim	9,648
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 216
IBNR	$ 143
Cumulative Number of Claims | claim	4,081