Consolidated Statements of Changes in Equity (Unaudited) - NPC - USD ($) $ in Millions	Total	Additional Paid-in Capital	NPC	NPC Common Stock	NPC Additional Paid-in Capital	NPC Retained Earnings	NPC Accumulated Other Comprehensive (Loss) Income, Net
Balance (shares) at Dec. 31, 2019				1,000
Balance at Dec. 31, 2019			$ 2,797	$ 0	$ 2,308	$ 493	$ (4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 4,628		273			273
Dividends declared			(85)			(85)
Other equity transactions	0	$ (1)	1			1
Balance (shares) at Sep. 30, 2020				1,000
Balance at Sep. 30, 2020			2,986	$ 0	2,308	682	(4)
Balance (shares) at Jun. 30, 2020				1,000
Balance at Jun. 30, 2020			2,792	$ 0	2,308	488	(4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	2,842		194			194
Other equity transactions	$ 1
Balance (shares) at Sep. 30, 2020				1,000
Balance at Sep. 30, 2020			$ 2,986	$ 0	2,308	682	(4)
Balance (shares) at Dec. 31, 2020	76,000,000		1,000	1,000
Balance at Dec. 31, 2020	$ 43,010		$ 2,939	$ 0	2,308	634	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	4,207		301			301
Dividends declared			$ (13)			(13)
Other equity transactions	$ (3)
Balance (shares) at Sep. 30, 2021	76,000,000		1,000	1,000
Balance at Sep. 30, 2021	$ 45,692		$ 3,227	$ 0	2,308	922	(3)
Balance (shares) at Jun. 30, 2021				1,000
Balance at Jun. 30, 2021			3,010	$ 0	2,308	705	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	1,922		$ 217			217
Other equity transactions	$ (2)
Balance (shares) at Sep. 30, 2021	76,000,000		1,000	1,000
Balance at Sep. 30, 2021	$ 45,692		$ 3,227	$ 0	$ 2,308	$ 922	$ (3)