Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Commercial - General Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - General Liability - Commercial $ in Millions	Dec. 31, 2021 USD ($) claim	Dec. 31, 2020 USD ($)	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	$ 6,670
IBNR	2,006
2012
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	632	$ 632	$ 630	$ 635	$ 635	$ 619	$ 636	$ 639	$ 611	$ 587
IBNR	$ 20
Cumulative Number of Claims | claim	35,313
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 624	623	620	623	613	655	650	655	$ 650
IBNR	$ 24
Cumulative Number of Claims | claim	33,706
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 659	659	658	635	631	654	658	$ 653
IBNR	$ 28
Cumulative Number of Claims | claim	28,064
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 617	602	600	589	574	576	$ 581
IBNR	$ 42
Cumulative Number of Claims | claim	24,118
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 683	673	671	667	659	$ 623
IBNR	$ 68
Cumulative Number of Claims | claim	24,511
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 630	634	632	632	$ 632
IBNR	$ 67
Cumulative Number of Claims | claim	22,195
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 639	646	644	$ 653
IBNR	$ 205
Cumulative Number of Claims | claim	19,917
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 682	682	$ 680
IBNR	$ 330
Cumulative Number of Claims | claim	18,602
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 722	$ 723
IBNR	$ 516
Cumulative Number of Claims | claim	13,028
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 782
IBNR	$ 706
Cumulative Number of Claims | claim	9,759