Consolidated Statement of Shareholder's Interest - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Shareholder's Interest [Roll Forward]
Balance at beginning of period			$ 12,803	$ 11,713
Shareholder's Interest Attributable to Noncontrolling Interest			0	1
Total Shareholder's Interest			12,803	11,714
Net income	$ 414	$ 386	1,193	1,040
Net Income (Loss) Attributable to Noncontrolling Interest			0	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest			1,193	1,040
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent			485	(41)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest			0	0
Other Comprehensive Income (Loss), Net of Tax	204	(72)	485	(41)
Distributions			(406)	(1)
Balance at end of period	14,084	12,712	14,084	12,712
Shareholder's Interest Attributable to Noncontrolling Interest	0	0	0	0
Total Shareholder's Interest	14,084	12,712	14,084	12,712
Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	9		9
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
Distributions			0	0
Balance at end of period	5,227	5,227	5,227	5,227
Shareholder's Interest [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	0		0
Accumulated Other Comprehensive Income/(Loss) [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period			(890)	(607)
Net income			0	0
Other Comprehensive Income (Loss), Net of Tax	204	(72)	485	(41)
Distributions			0	0
Balance at end of period	(405)	(648)	(405)	(648)
Accumulated Other Comprehensive Income/(Loss) [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	0		0
Retained Earnings [Member]
Shareholder's Interest [Roll Forward]
Balance at beginning of period			8,466	7,093
Net income			1,193	1,040
Other Comprehensive Income (Loss), Net of Tax			0	0
Distributions			(406)	0
Balance at end of period	9,262	$ 8,133	9,262	8,133
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	9		9
Parent [Member]
Shareholder's Interest [Roll Forward]
Distributions			(406)	0
Parent [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	9		9
Noncontrolling Interest [Member]
Shareholder's Interest [Roll Forward]
Distributions			0	$ (1)
Noncontrolling Interest [Member] | Accounting Standards Update 2014-09 [Member]
Shareholder's Interest [Roll Forward]
Adoption of accounting standards	$ 0		$ 0