Insurance (Rollforward of Unpaid Claims) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Balance at January 1,	$ 16,157	$ 9,669	$ 9,525
Less: Reinsurance recoverables	1,968	476	454
Net Balance at January 1,	14,189	14,012	9,071
Incurred related to:
Current year	24,370	24,011	9,533
Prior years	133	382	(78)
Total incurred	24,503	24,393	9,455
Paid related to:
Current year	(18,525)	(18,696)	(6,759)
Prior years	(5,271)	(5,520)	(2,574)
Total paid	(23,796)	(24,216)	(9,333)
Net Balance at December 31,	14,896	14,189	14,012
Add: Reinsurance recoverables	2,198	1,968	476
Balance at December 31,	17,094	16,157	9,669
Scenario, Previously Reported
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance at January 1,	14,189	9,193	9,071
Paid related to:
Net Balance at December 31,		14,189	9,193
Cumulative adjustment
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance at January 1,	0	4,819	0
Paid related to:
Net Balance at December 31,		0	$ 4,819
Restatement Adjustment
Liability for Claims and Claims Adjustment Expense [Line Items]
Less: Reinsurance recoverables	742
Net Balance at January 1,	$ 736
Paid related to:
Net Balance at December 31,		736
Add: Reinsurance recoverables		$ 742