Derivative Financial Instruments - Gross and Net Amounts Derivatives (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Asset derivatives
Gross amount	$ 84	$ 115
Counter- party netting	0	0
Total asset derivatives	84	115
Liability derivatives
Gross amount	(303)	(346)
Counter- party netting	4	3
Total liability derivatives	(299)	(343)
OTC derivatives
Asset derivatives
Gross amount	4	4
Counter- party netting	(4)	(3)
Cash collateral (received) pledged	0	0
Total asset derivatives	0	1
Securities collateral (received) pledged	0	0
Net amount	0	1
Liability derivatives
Gross amount	(9)	(10)
Counter- party netting	4	3
Cash collateral (received) pledged	1	(2)
Total liability derivatives	(4)	(9)
Securities collateral (received) pledged	2	3
Net amount	$ (2)	$ (6)