Consolidated Statement of Shareholder's Interest - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Shareholder's Interest [Roll Forward]
Balance at beginning of period			$ 15,884	$ 12,803
Net income	$ 479	$ 446	1,180	779
Other Comprehensive Income (Loss), Net of Tax			(251)	281
Cumulative Effect of New Accounting Principle in Period of Adoption		9		9
Distributions declared			(1,463)	(28)
Balance at end of period	15,350	13,844	15,350	13,844
Shareholder's Interest [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period			5,227	5,227
Net income			0	0
Other Comprehensive Income (Loss), Net of Tax			0	0
Cumulative Effect of New Accounting Principle in Period of Adoption		0		0
Distributions declared			0	0
Balance at end of period	5,227	5,227	5,227	5,227
Accumulated Other Comprehensive Income/(Loss) (Note11) [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period			(419)	(890)
Net income			0	0
Other Comprehensive Income (Loss), Net of Tax			(251)	281
Distributions declared			0	0
Balance at end of period	(670)	(609)	(670)	(609)
Accumulated Other Comprehensive Income/(Loss) (Note11) [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption		0		0
Retained Earnings [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period			11,076	8,466
Net income			1,180	779
Other Comprehensive Income (Loss), Net of Tax			0	0
Distributions declared			(1,463)	(28)
Balance at end of period	$ 10,793	9,226	$ 10,793	9,226
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption		$ 9		$ 9