Insurance (Rollforward of Unpaid Claims) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Balance at beginning of period	$ 16,151	$ 9,669
Less: Reinsurance recoverables	1,226	476
Net Balance, beginning of period	14,925	14,090
Incurred related to:
Current period	18,028	18,157
Prior years	156	147
Total incurred	18,184	18,304
Paid related to:
Current period	(13,880)	(12,818)
Prior periods	(4,213)	(4,620)
Total paid	(18,093)	(17,438)
Net Balance, end of period	15,016	14,956
Add: Reinsurance recoverables	2,205	2,052
Balance at end of period (included in future policy benefits and other policy-related balances)	17,221	17,008
Scenario, Previously Reported
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance, beginning of period	14,925	9,193
Cumulative adjustment
Liability for Claims and Claims Adjustment Expense [Line Items]
Net Balance, beginning of period	$ 0	$ 4,897