Fair Value Measurements - Changes in balances of Level 3 financial liabilities carried at fair value (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial liabilities, Beginning Balance		$ (1,963)	$ (1,450)	$ (1,759)	$ (1,369)
Total realized/unrealized gains (losses) included in Net income		(112)	(62)	(259)	(79)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0	0
Purchases and issuances		(80)	(72)	(159)	(154)
Sales and settlements		26	27	48	45
Transfer into Level 3		0	0	0	0
Transfer out of Level 3		0	0	0	0
Financial liabilities, Ending Balance	[1]	(2,129)	(1,557)	(2,129)	(1,557)
Embedded derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial liabilities, Beginning Balance		(1,963)	(1,450)	(1,759)	(1,369)
Total realized/unrealized gains (losses) included in Net income		(112)	(62)	(259)	(79)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)		0	0	0	0
Purchases and issuances		(80)	(72)	(159)	(154)
Sales and settlements		26	27	48	45
Transfer into Level 3		0	0	0	0
Transfer out of Level 3		0	0	0	0
Financial liabilities, Ending Balance		$ (2,129)	$ (1,557)	$ (2,129)	$ (1,557)

[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.