Fair Value Measurements - Changes in balances of Level 3 financial liabilities carried at fair value (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial liabilities, Beginning Balance		$ (2,129)	$ (1,557)	$ (1,759)	$ (1,369)
Total realized/unrealized gains (losses) included in Net income		(127)	(109)	(386)	(188)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0	0
Purchases and issuances		(65)	(53)	(224)	(207)
Sales and settlements		28	31	76	76
Transfer into Level 3		0	0	0	0
Transfer out of Level 3		0	0	0	0
Financial liabilities, Ending Balance	[1],[2]	(2,293)	(1,688)	(2,293)	(1,688)
Embedded derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial liabilities, Beginning Balance		(2,129)	(1,557)	(1,759)	(1,369)
Total realized/unrealized gains (losses) included in Net income		(127)	(109)	(386)	(188)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0	0
Purchases and issuances		(65)	(53)	(224)	(207)
Sales and settlements		28	31	76	76
Transfer into Level 3		0	0	0	0
Transfer out of Level 3		0	0	0	0
Financial liabilities, Ending Balance		$ (2,293)	$ (1,688)	$ (2,293)	$ (1,688)

[1] As discussed previously, these tables exclude the portion of MIE liabilities allocated to Level 3, which are derived from the fair value of the MIE assets.

[2] As discussed previously, these tables exclude the portion of MIE liabilities allocated to Level 3, which are derived from the fair value of the MIE assets.