Insurance (Rollforward of Unpaid Claims) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Balance at January 1,	$ 19,216	$ 17,788	$ 17,094
Less: Reinsurance recoverables	2,377	2,332	2,198
Net Balance at January 1,	16,839	15,456	14,896
Incurred related to:
Current year	27,272	27,093	24,571
Prior years	192	313	454
Total incurred	27,464	27,406	25,025
Paid related to:
Current year	(20,230)	(20,141)	(18,757)
Prior years	(6,241)	(5,882)	(5,708)
Total paid	(26,471)	(26,023)	(24,465)
Total unpaid claims and allocated claims adjustment expense	13,554
Net Balance at December 31,	16,174	16,839	15,456
Add: Reinsurance recoverables	2,417	2,377	2,332
Balance at December 31,	18,591	19,216	17,788
Metropolitan Property And Casualty Insurance Company [Member]
Paid related to:
Total unpaid claims and allocated claims adjustment expense	$ (1,658)	$ 0	$ 0