Consolidated Statements of Changes in Equity - USD ($) $ in Millions	Total	Member's Equity	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2016			$ 119
Cash distributions	$ (1,425)
Comprehensive income (loss), net of tax	1,794
Balance at Jun. 30, 2017			117
Cumulative Effect of New Accounting Principle in Period of Adoption | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]	(3)	$ (3)	0
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	0	(1)	1
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Domain]	0	(26)	26
Balance at Dec. 31, 2017	43,009	42,778	231
Cash distributions	(2,275)	(2,275)	0
Comprehensive income (loss), net of tax	2,455	2,454	1
Balance at Jun. 30, 2018	$ 43,186	$ 42,929	$ 257