Reserve for Unpaid Losses and Loss Adjustment Expenses - P&C Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 32,287
Less: payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross	33,029	$ 32,287
Reinsurance recoverables, net	4,357	4,061
Property and Casualty Insurance Products
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	23,775	22,545	$ 22,568
Reinsurance and other recoverables	3,957	3,488	3,625
Beginning liabilities for unpaid losses and loss adjustment expenses, net	19,818	19,057	18,943
Add: Maxum acquisition	0	0	122
Provision for unpaid losses and loss adjustment expenses
Current accident year	7,107	7,381	6,990
Prior accident year development	(167)	(41)	457
Total provision for unpaid losses and loss adjustment expenses	6,940	7,340	7,447
Less: payments
Current accident year	2,452	2,751	2,749
Prior accident years	3,954	3,828	4,219
Total payments	6,406	6,579	6,968
Less: net reserves transferred to liabilities held for sale	0	0	487
Ending liabilities for unpaid losses and loss adjustment expenses, net	20,352	19,818	19,057
Reinsurance and other recoverables	4,232	3,957	3,488
Ending liabilities for unpaid losses and loss adjustment expenses, gross	$ 24,584	$ 23,775	$ 22,545