Reserve for Unpaid Losses and Loss Adjustment Expenses - P&C Liabilities for Unpaid Losses and Loss Adjustment Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	$ 36,517
Less: payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross	36,582
Property, Liability and Casualty Insurance Product Line
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross	28,261	$ 24,584
Reinsurance and other recoverables			$ 5,332	$ 5,275	$ 4,209	$ 4,232
Beginning liabilities for unpaid losses and loss adjustment expenses, net	23,048	20,402	$ 23,048	$ 22,986	$ 20,402	$ 20,352
Provision for unpaid losses and loss adjustment expense
Current accident year	1,883	1,641
Prior accident year development [1]	23	(11)
Total provision for unpaid losses and loss adjustment expenses	1,906	1,630
Less: payments
Current accident year	304	271
Prior accident years	1,491	1,309
Total payments	1,795	1,580
Foreign currency adjustment	(20)	0
Ending liabilities for unpaid losses and loss adjustment expenses, net	23,048	20,402
Ending liabilities for unpaid losses and loss adjustment expenses, gross	28,380	24,611
Property, Liability and Casualty Insurance Product Line | Adverse Development Cover Navigators Group [Member]
Provision for unpaid losses and loss adjustment expense
Deferred Revenue	$ 29	$ 0