Reserve for Property and Casualty Insurance Claims and Claims Expense - Reconciliation of the net incurred and paid claims development (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Claims Development [Line Items]
Net outstanding liabilities	$ 20,577
ULAE	1,484
Recoverables	7,033
ULAE	41
Gross reserve for property and casualty insurance claims and claims expense	27,610	$ 27,712	$ 27,423
Discontinued Lines and Coverages
Claims Development [Line Items]
Net outstanding liabilities	1,330
Recoverables	479
Gross reserve for property and casualty insurance claims and claims expense	695
Auto insurance - liability coverage
Claims Development [Line Items]
Net outstanding liabilities	12,789
Recoverables	5,979
Auto insurance - physical damage coverage
Claims Development [Line Items]
Net outstanding liabilities	373
Recoverables	4
Homeowners insurance
Claims Development [Line Items]
Net outstanding liabilities	2,104
Recoverables	171
Other personal lines
Claims Development [Line Items]
Net outstanding liabilities	1,335
Recoverables	153
Commercial lines
Claims Development [Line Items]
Net outstanding liabilities	1,132
Recoverables	196
Protection Services
Claims Development [Line Items]
Net outstanding liabilities	30
Recoverables	$ 10